Determining the true incidence of developmental dysplasia of the hip (DDH) can be difficult due to disparities in its definition, heterogeneous clinical examination methods, varying examiner skills, and clinical setting¹⁾. In some cases, dysplastic hips in neonates can become nondysplastic over time. However, the estimated incidence of DDH is 3-5 per 1,000 live births¹⁾. Irrespective of treatment, in some cases a dysplastic hip can become arthritic in adults²⁾. Several classification schemes have been described for DDH^3,4). Total hip arthroplasty (THA) is the most successful and accepted option for treatment of arthritic DDH in adults³⁾. However, successful THA in high-riding hips requires performance of supplementary procedures (Crowe III and IV). Some studies have described staged and nonstaged supplementary procedures involving THA for treatment of this type of hip^5-7). Subtrochanteric shortening derotation osteotomy (SSDO) with THA is a nonstaged option for treatment of this type of arthritic high-riding DDH⁸⁾. Successful outcomes have been attained after modular/monoblock femoral stem surgery and cemented/cementless arthroplasty for patients with difficult-to-reduce hips^9-11). Li et al.¹²⁾ reviewed the outcomes of using different subtrochanteric osteotomy designs with THR in high-riding hips. However, the studies included in their review had a follow-up of as little as three months⁸⁾. Data regarding outcomes and prosthesis survival from short-term follow-up studies could be misleading. We noted that the authors of the review included cemented and cementless prostheses, further adding to heterogeneity^10,11). Since conduct of their review, we have identified 16 additional studies with mid- and long-term follow-up following SSDO with THA for DDH^9,10,13-26). Therefore, a review of SSDO with THA for arthritic DDH in adults was conducted. The primary objective of this review registered (PROSPERO, No. CRD42023405273) was to examine nonunion rates in patients with arthritic DDH treated with THA and SSDO; however, based on sporadic rates of nonunion and the type of included studies, our primary objective was revised for comparison and analysis of the outcomes for adult patients with arthritic DDH after SSDO with cementless hip arthroplasty between monoblock and modular femoral stems at a minimum follow-up of five years.

The procedures described in this review were performed according to the ethical standards of the responsible committee on human experimentation (institutional and national). This review was registered with PROSPERO (No. CRD42023405273) and followed PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines²⁷⁾. The review protocol at PROSPERO was modified due to the analysability of studies for subgroup analysis between monoblock and modular stems.

1. Eligibility Criteria (Inclusion and Exclusion Criteria)

1) Inclusion criteria

Studies published in English that evaluated functional and radiological outcomes and complications after SSDO with cementless THA in adults (18 years or more) with a minimum follow-up period of five years were included. For this review, the mid and long-term follow-up durations were defined as five and 10 years, respectively. Studies were included irrespective of the Crowe type and femoral stem design (monoblock, modular, or both). Comparative studies where one or both arms included SSDO with cementless components among DDH hips were included in this review.

2) Exclusion criteria

Studies on arthritis of the hip arthritis after nondysplastic dislocations (septic, traumatic, or neglected) were excluded from this review, and case series and case reports were also excluded. A case series was defined as one that included fewer than ten SSDOs treated with THA. Studies that included fewer hips when overlapping patient populations, study designs, and settings were excluded²⁸⁾. Mixed studies of SSDO and THA as one of several treatment methods, staged THA, the effects of implant designs among high-riding hips without SSDO, and studies combining distal femoral osteotomy with THA among DDH patients were excluded.

2. Information Sources

A search of the major electronic databases was conducted for identification of studies in the English language on the effects of SSDO with cementless THA in patients with arthritis secondary to DDH.

3. Search Strategy

A search of the Cochrane Library, Embase, PubMed, ProQuest, and Scopus on June 15, 2023 was conducted. The search strategy for electronic databases used in this review is described in Appendix 1. A hand-search of references from the included studies was performed, and reports from trial registries, conference proceedings, books, and dissertations were excluded.

4. Selection Process

All search results were imported into the Rayyan AI systematic review website, and titles and abstracts were screened independently for potentially eligible studies by the review authors A.M. and A.R. The authors obtained full-text reports where appropriate. The study selection was performed independently by the same review authors. To ensure a consensus, disagreements regarding the inclusion or exclusion of individual studies and data extraction were resolved by discussion between the two authors or with a third author (S.K.N.) for the final study selection. Data including the study design, population, interventions, outcome measures, and results were collected. We did not mask the source or authorship of the trial reports.

5. Study Selection

A total of 1,149 records up to May 2023 for studies on SSDO with THA among DDH patients were searched. Our study assessment plan is as follows:

1) Twenty-five studies (23 from electronic databases and two from references) meeting our inclusion criteria were isolated^{9,10,13-26,28-36)}.

2) Five studies were excluded from the qualitative and quantitative analysis^28,33-36). The PRISMA flow diagram shows the reasons for excluding studies from the review²⁷⁾ (Fig. 1).

Figure 1. PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) flow diagram for the review²⁷⁾. DDH: developmental dysplasia of the hip.

3) Analysis of 20 studies was performed for qualitative analysis and quantitative synthesis^{9,10,13-26,29-32)}.

4) Analysis of 14 studies was performed for sensitivity analysis by eliminating studies other than exclusive Crowe IV cases^{9,10,13,15-17,20,22-26,29,31)}. The studies were divided into three groups based on femoral stem type (group 1: modular stem, group 2: monoblock stem, group 3: both stems).

5) Eight^{9,13-17,29,30)}, eleven^{10,18-25,31,32)}, and one²⁶⁾ studies were classified according to groups 1, 2, and 3, respectively.

6. Data Items (Outcome Measures)

The following characteristics were recorded from the included reports:

1) Demographic outcomes (age, sex, bilateral operation).

2) Functional outcome scores for a primary hip arthroplasty before and after the operation (Harris hip score, Merle d’Aubigné score).

3) THA type of implant and bearing surface and fixation modes of the SSDO site.

4) Survivorship

5) Radiographic outcomes: (A) Eight^{9,16,17,22-25,29)} and 7 studies^{13,15-17,19,20,26)} evaluated stem integration based on the criteria reported by Engh et al.³⁷⁾ and Gruen zones³⁸⁾, while analysis of cup integration based on the criteria reported by DeLee and Charnley³⁹⁾ was performed for 13 studies^{10,13-15,17-20,22-25,32)}. Stem align-ment was reported in two studies^25,29) according to neutral and slight varus by Christie et al.⁴⁰⁾.

6) Complications: (A) Dislocations early or late based on the duration of their occurrence within six weeks or more after the operation. (B) Controlled/uncontrolled fractures based on operating surgeon-directed intentional fractures in the proximal femur for negotiating a disproportionate stem to the femoral canal or displaced/undisplaced unintentional cracks that occurred during bone preparation. (C) Nonunion. (D) Nerve palsy (sciatic/obturator/femoral). (E) Revision for any reason.

7. Assessment of Risk of Bias in the Included Studies

The Joanna Briggs Institute (JBI) critical appraisal tool was used in conduct of the systematic reviews: Checklist for Analytical Cross-Sectional Studies for risk of bias assessment⁴¹⁾. The JBI: Checklist for Analytical Cross-Sectional Studies is an eight-item scale. All questions were answered as yes/no/unclear/not applicable. Mail was sent to the authors of the included studies for question. 1. Were confounding factors identified? 2. Were strategies for managing confounding factors stated?

8. Effect Measures

A meta-analysis of the included studies was performed using RevMan 5.4. The random effects model was used to pool the mean difference between the Harris hip scores before and after the operation. However, the incidence of nonunion, dislocations, controlled and uncontrolled femur fractures, nerve paralysis, and revisions due to any cause in groups 1, 2, and 3 was estimated. A subgroup analysis was performed for estimating the difference in outcomes between groups 1 and 2 after the operation. Estimation of heterogeneity and inconsistency across the included studies was performed using the chi-square test and I² test. The results of subgroup analysis of pooled estimates of the mean difference in Harris hip score before and after the operation among groups were graphically represented using a forest plot. A sensitivity analysis was performed to determine the pooled estimate after excluding studies other than exclusive Crowe IV cases to estimate the effects of THA combined with SSDO in patients with high-riding DDH. A test for bias in the results of meta-analysis was performed and is represented as a funnel plot. Statistical assessments were performed by the author of the review (S.K.N.).

1. Qualitative Analysis

A summary of demographic and functional outcomes and complications is shown in Table 1. Five and seven studies were reported from China^9,15-17,22) and Türkiye^{10,18,19,21,23-25)}. Two studies were reported from the USA^14,30), Italy^20,26), and Japan^29,31). One study each was reported from Norway³²⁾ and the Czech Republic and Slovakia¹³⁾. Three^29,30,32), 13^{9,10,13,15-17,19-22,25,26,31)}, and four^14,18,23,24) studies were published between 2000-2010, 2011-2020, and 2021-2023, respectively. All except for one study were retrospective single-arm studies. One comparative retrospective study evaluated patients treated with trochanteric osteotomy and SSDO²¹⁾. Data from the SSDO arm of the study were pooled into this review. Recruitment of patients was heterogeneous among the studies in groups 1, 2, and 3. All but two studies^14,30) included Crowe IV hips in group 1. Seven studies^{10,20,22-25,31)} in group 2 and one study²⁶⁾ in group 3 included exclusive Crowe IV hips. The hip was approached using the posterolateral and Hardinge approaches in 16^{9,10,13,15-21,23,24,29-32)} and three^22,25,26) studies, respectively. Eleven, four, one, and two transverse^{9,10,13,15-17,19,20,23,24,30)}, step cut^18,25,29,31), chevron²²⁾, and mixed osteotomy studies were included in this review^26,32). Application of structural autografts from the resected femoral head was reported in 94 hips in seven studies^{17,20-22,29-31)}. Two studies reported the use of medial acetabular wall osteotomy to restore the centre of rotation in high-riding hips^10,32). The Harris hip score was used for assessment of functional outcomes before and after the operation in seven, 10, and one studies in groups 1^9,13-17,30), 2^10,18-25,31), 3²⁶⁾, respectively. Functional hip assessments before and after surgery were reported using the Harris hip score. In one study, the Harris hip score was not reported preoperatively for patients in group 2³¹⁾. Nine studies^{13,15-17,19,23-25,41)} evaluated functional outcomes according to Merle d’Aubigné and Postel scores, the Western Ontario and McMaster University Osteoarthritis Index (WOMAC) score, University of California, Los Angeles activity score (UCLA), patient satisfaction, 36-Item Short Form Health Survey (SF-36), 12-Item Short Form Health Survey (SF-12), and Hip Dysfunction and Osteoarthritis Outcome Score (HOOS). Results of the Trendlenberg test before and after the operation were reported by seven, seven, and one study from groups 1^9,13-17,29), 2^{18,19,21,25,31,32,34)}, and 3²⁶⁾, respectively.

Table 1 . Comparative Summary of Demographic Outcomes, Functional Outcomes and Complications between Groups 1, 2 and 3.

Parameter	Group 1 (modular stem)	Group 2 (monoblock stem)	Group 3 (mixed)	All
Demographic outcome measures
No. of studies	8	11	1	20
No. of patients	244	478	15	737
No. of hips	292	622	17	931
Male	34	80	10	124
Female	210	398	5	613
Unilateral	174	361	13	548
Bilateral	48	148	2	198
Crowe I/II/III/IV*	8/5/9/265	0/0/58/520	0/0/0/17	8/5/67/802
Mean age (yr)	45±7.2 (37-60)	47.12±6.18 (40.5-58.5)	38.6 (28-68)	46.04±6.55 (36.6-60)
Mean follow-up (yr)	10±4 (8-19)	8.9±2.4 (5.7-13)	7.3 (5.3-11.1)	9.33±2.92 (5.7-19)
Functional outcome measures
Preoperative HHS†	34.68±14.58 (21-65)	37.36±14.92 (15-78)	38.3 (32-52)	36.34±14.05 (15-78)
Postoperative HHS	74.36±30.36 (52-98)	89.10±3.61 (59-100)	85.6 (69-90)	83.03±19.99 (52±100)
Preoperative HHS rating‡ (excellent/good/fair/poor)	0/0/0/189	0/5/1/143	-	0/5/1/332
Postoperative HHS rating (excellent/good/fair/poor)	72/100/14/1	181/43/20/7‡	-	253/143/34/8
Complication
Dislocations	19 (6.5)	27 (4.3)	-	46
Nerve paralysis	5 (1.7)	10 (1.6)	2 (11.8)	17
Heterotopic ossification (Brooker grades)	2/3/1/0 (2.1)	22/6/5/2 (5.6)	-	41
Revision due to any cause	23 (7.9)	46 (7.4)	-	69
Uncontrolled femur fractures	23 (7.9)	26 (4.2)	1 (5.9)	50
Controlled femur fractures	0 (0)	103 (16.6)	-	103
Nonunion	1 (0.3)	12 (1.9)	-	13

Values are presented as number only, mean±standard deviation (range), or number (%)..

HHS: Harris hip score..

*One study did not divide 65 dysplastic hips per any existing classification schemes³²⁾..

^†The HHS assessed functional outcomes before and after operation in 7, 10, and 1 study in group 1^9,13-17,30), 2^10,18-25,31), and 3²⁶⁾, respectively..

^‡Two studies rated 57 hips excellent or good in follow-up for HHS rating^25,31) while one study rated 58/29/11/4 as excellent/good/fair/poor postoperatively in group 2²⁰⁾..

2. Outcomes of Risk of Bias Assessment

Six^{13-15,17,29,30)} and two^9,16) studies showed high and moderate risk of bias in group 1. Five^10,18-20,22) and six^{21,23-25,31,32)} studies showed high and moderate risk of bias in group 2. In one study high risk of bias was observed in group 3²⁶⁾. One investigator discussed the presence of confounders²¹⁾.

1) Nine studies did not describe the criteria for inclusion in the sample^{9,10,14,16,17,19,20,29,30)}.

2) Six studies did not describe the study settings^{19-21,25,30,32)}. The authors of the study selected records from the arthroplasty registry, and a set of patients meeting inclusion criteria were included in the study.

3) Six reports were unclear on study settings^{19-21,25,30,32)}.

4) We received a reply from one study investigator who indicated the presence of confounders²¹⁾.

5) Eight studies were unclear on valid and reliable measurement of outcomes of survival analysis^{10,13-15,17,18,22,26)}.

6) Two studies did not use appropriate statistical methods for reporting results^26,32).

A graphical representation of the publication bias test was generated through a funnel plot, which showed the symmetric distribution of the effect estimate, indicating the absence of publication bias (Fig. 2).

Figure 2. Funnel plot of studies included in the review. SE: standard error, MD: mean deviation.

3. Quantitative Analysis (Meta-analysis)

The mean difference in the Harris hip score before and after the operation pooled from 17 studies^{9,10,13-26,31)} was 47.55 (95% confidence interval [CI] 43.16, 51.94) (Fig. 3). The mean differences in Harris hip scores before and after surgery in groups one^{9,13-17,29,30)}, two^{10,18-25,31,32)}, and three²⁶⁾ were 46.59 (95% CI 41.67, 51.51), 48.24 (95% CI 41.37, 55.11), and 47.30 (95% CI 43.85, 50.75), respectively (Fig. 4). The results of sensitivity analysis by eliminating non-Crowe IV hips showed a mean difference in Harris hip scores before and after surgery in groups 1^{9,13,15-17,29)}, 2^{10,20,22-25,31)}, and 3²⁶⁾ of 49.33 (95% CI 47.97, 50.69), 49.93 (95% CI 48.70, 51.16), and 47.30 (95% CI 43.85, 50.75), respectively (Fig. 5). Persistence of limpness after the operation was reported in 22% and 50% of the pooled cases in groups 1 and 2 after the operation. After the operation, the Trendelenburg test showed demonstrable results in 11% and 20% of the patients in groups 1 and 2. The union time for the osteotomy site was comparable at 4.2±2.79 months (range, 2-12 months) and 2.76±2.66 months (range, 2-12 months) in groups 1 and 2. The correction of limb length discrepancy (LLD) (shortening) was also comparable in groups 1 and 2, while the LLD corrected from 45.96±5.19 to 13.85±7.73 mm in group 1 was 41.77±9.41 to 12.4±2.33 mm in group 2. Shortening at the osteotomy site was 35.66±6.85 mm and 34.88±6.43 mm in groups 1 and 2, which was comparable.

Figure 3. Pooled estimate of the effect of mean difference in Harris hip score before and after the operation in the included studies. SD: standard deviation, CI: confidence interval.

Figure 4. Pooled estimate of the effect of mean difference in Harris hip score before and after the operation between groups 1, 2, and 3. SD: standard deviation, CI: confidence interval.

Figure 5. Sensitivity analysis after excluding non-Crowe IV hips. SD: standard deviation, CI: confidence interval.

4. Implant Characteristics and Fixation Modes

A summary of the stem and cup types from the individual studies included in this review is shown in Table 2. Cables/plates/titanium bands/claw plates were used in groups 1 and 2 for treatment of displaced or nondisplaced fractures in the dysplastic femur during preparation of the femoral canal. The stems were stabilized using cables in patients with controlled or uncontrolled femoral fractures. Bone grafting of the osteotomy site was also performed with or without cable fixation in groups 1 and 2 in most studies.

Table 2 . Summary of Stem and Cup Types in the Included Studies.

Study	Type of cup	Cup diameter (mm)	Type of stem	Head size	Bearing
Group 1 (n=8)
Bernasek et al.30)	APR=6 InterOp=7 S-ROM=5 Duraloc TriSpike=1 Hyalamer=1 Pinnacle=1 Trident=2	Mean 46 (40-55)	Type 5 modular stem (DePuy S-ROM)	-	Metal on polyethylene
Sun et al.9)	DePuy Pinnacle	Not available	Type 5 modular stem (S-ROM DePuy titanium)	-	Metal on polyethylene
Necas et al.13)	DePuy Pinnacle cementless hemispherical press fit cup	Mean 44 (38-52)	Type 5 modular stem (DePuy S-ROM)	22 mm=6 28 mm=3 36 mm=4 All cobalt chromium heads 28 mm=15 All ceramic heads	UHMWPE liner=9 Ceramic liner=15
Palumbo et al.14)	Howmedica=1 Stryker Trident=2 DePuy Duraloc TriSpike=1 DePuy Pinnacle=1 DePuy One Piece=1 DePuy S-ROM=6 Sulzer APR=4 Sulzer InterOp=8	Range 40-55	Type 5 modular stem distally fluted and proximally porous coated (DePuy Warsaw)	22 mm=20 28 mm=4	Metal on polyethylene
Takao et al.29)	ZTT cup=24 Triology acetabulum system=9	Median 42 (40-48)	Type 5 modular stem (DePuy S-ROM)	22 mm=18 (cobalt chromium) 26 mm=12 28 mm=3	UHMWPE liner=24 hips and metal head Highly crosslinked polyethylene liner=9 and metal head
Liu et al.15)	Duroloc cup	Range 40-48	Type 5 modular stem (S-ROM DePuy titanium)	22 mm=17 28 mm=4	Metal on polyethylene
Wang et al.16)	DePuy Pinnacle cup	Median 42 (40-46)	Type 5 modular femoral stem (S-ROM, DePuy)	28 mm=34 32 mm=30 36 mm=12	Ceramic on ceramic=60 hips Metal on Polyethylene=16 hips
Zeng et al.17)	DePuy Pinnacle cup	Not available	Type 5 modular stem (S-ROM DePuy titanium)	-	Ceramic on ceramic=49 Ceramic on polyethylene=3
Group 2 (n=11)
Biçici et al.18)	EP fit plus=9 POLAR cup dual mobility=28	EP fit plus cup, median 42 (40-46) POLAR dual mobility cup, median 43 (43-47)	Type 3 C monoblock stem SL plus=30 Synergy=7	-	-
Desteli et al.19)	Not reported	Range 40-48	Type 2 monoblock stem Secur-Fit femoral stem=40 Type 2 with distal flutes Secur-Fit plus stem=20	-	Ceramic on ceramic=24 Metal on polyethylene=36
Erdem et al.10)	EP-Fit Plus REXPOL cup=26	40=16 42=10	Type 3 C monoblock stem SL-Plus=26	22 mm=26	Metal on polyethylene
Grappiolo et al.20)	Harris Triology=66 Delta TT=29 Delta PF=1 Delta Custom=1 Delta Motion=2 CLS Spotorno=2	42=8 44=43 46=28 48=16 50=5 52=2	Type 3 B monoblock Wagner cone stem=102	22 mm=18 28 mm=43 32 mm=39 36 mm=2	Metal on polyethylene=31 Ceramic on polyethylene=36 Ceramic on ceramic=35
Hasegawa et al.31)	Dual-geometry sockets, TriAD, and Trident (Stryker)	40=2 42=4 44=9 46=3 48=2	Type 2 monoblock stem Secur-Fit=6 Type 2 monoblock stem super Secur-Fit=7 J stem=2 Omniflex stem=2 C stem=2 Normalised stem=1	22 mm=9 26 mm=10 28 mm=1	Metal on polyethylene
Karaismailoglu and Karaismailoglu21)	-	-	-	-	-
Li et al.22)	Duraloc sector cup=8 PressFIT SII cup=10 Reflection cup=4	Median 46 (42-48)	Monoblock stem Anatomic medullary Stem summit stem=4, ribbed stem=10, synergy stem=4	22 or 28 mm	Cobalt chromium metal and UHMWPE=10 Ceramic and UHMWPE=12
Caylak et al.24)	Biolox Aluminium insert=19 Biolox delta ceramic cup=48	42=2 44=1 46=47 48=15 50=2	CDH stem=34 Synergy=19 Wagner Cone=14	22 mm=2 28 mm=48 32 mm=17	Ceramic on ceramic=48 Metal on polyethylene=19
Ors et al.23)	Triology acetabular component (Zimmer)	Median 46 (42-52)	Type 3 B monoblock Wagner Cone femoral stem (Zimmer)	28 mm=76 32 mm=51	Ceramic on ceramic
Ozden et al.25)	Reflection ceramic interfit cup=45	46=45 hips	Anatomic metaphyseal fixation stem=22 Cylindrical diaphyseal stem=23	28 mm=45	Ceramic on ceramic
Reikerås et al.32)	Hemispheric cup (Landanger)		Monoblock titanium stem press-fit (Landanger)	-	Metal on polyethylene
Group 3 (n=1)
Rollo et al.26)	Allofit (Sulzer)=5 Bantam (DePuy Synthes)=12	Mean 42 (38-46)	Type 5 modular S-ROM=12 Monoblock CSR Japan=5	22 mm=11 28 mm=2 32 mm=4	Metal on polyethylene=15 Ceramic on ceramic=2

UHMWPE: ultrahigh molecular weight polyethylene..

5. Survivorship

The results of survivorship analysis for individual studies are shown in Table 3. Survivorship was not recorded by one study each in group 1¹⁷⁾, group 2¹⁹⁾, or group 3²⁶⁾. Estimation of survivorship was not performed using statistical methods in two studies in group 1^13,15) and three in group 2^10,18,22). Twelve studies^{9,14,16,20,21,23-25,29-32)} were heterogeneous in terms of the duration of follow-up, type of implant, and bearing surfaces used for survival analysis.

Table 3 . Survivorship Analysis of Included Studies in Groups 1, 2, and 3.

Study	Survivorship
Group 1 (n=8)
Bernasek et al.30)	Kaplan–Meier survivorship estimate with end point of revision due to any cause was 75% at 14 years (95% CI 55%-97%).
Sun et al.9)	Kaplan–Meier survivorship estimate with end point of revision due to any cause was 100% at mean follow-up of 10 years. Kaplan–Meier survivorship estimate with end point of revision for aseptic loosening, nonunion, mechanical failure or wear: was 100% at a mean follow-up of 10 years.
Necas et al.13)	Survivorship was not estimated by statistical methods but was reported almost 90% over an average of almost 8 years.
Palumbo et al.14)	Cumulative incidence survivorship with endpoint being revision due to any cause was 67% at the mean follow-up of 19±7 years.
Takao et al.29)	Kaplan–Meier survivorship estimate with end point of stem revision was 97% (95% CI 80%-99%) at 8 years. Kaplan–Meier survivorship estimate with end point of aseptic loosening of stem 97% (95% CI 80%-99%) at 8 years.
Liu et al.15)	Survivorship was not estimated by statistical methods. The 5-year prosthesis survival rate was 100%, and the 10-year prosthesis survival rate was 91.30%.
Wang et al.16)	Kaplan–Meier survivorship estimate with end point revision for any reason 97% (95% CI 84-99) at 10 years. Kaplan–Meier survivorship estimate with revision for radiographic loosening of any component 97% (95% CI 84-99) at 10 years.
Zeng et al.17)	THA survivorship was not estimated.
Group 2 (n=11)
Biçici et al.18)	Survivorship was not estimated using statistical methods however the authors reported a 97.2% survival at mean follow-up of 8.3 years (6-11 years).
Desteli et al.19)	Survivorship was not estimated.
Erdem et al.10)	Survivorship was not estimated by statistical methods however the authors reported 96% survival at a mean follow-up of 7.1 years.
Grappiolo et al.20)	Kaplan–Meier survivorship was estimated for revision of any component due to any cause and represented on a chart.
Hasegawa et al.31)	Kaplan–Meier survivorship with a cumulative survival rate and any implant revision as endpoint was 90.0% (95% CI 76.6-100) and 74.6% (95% CI 51.1-98.3) at 5 and 10 years.
Karaismailoglu and Karaismailoglu21)	Kaplan–Meier survivorship without endpoint and CIs was reported to be 96.1% at 5 years.
Li et al.22)	Survivorship was not estimated by statistical methods; however, the authors reported the radiographic signs of aseptic loosening recognized as the end point the survival rates of the femoral components were 100% at 5- to 10-year follow-up.
Caylak et al.24)	Kaplan–Meier survivorship estimate with end point revision for any reason was 94.5% (95% CI 90.5-98.5) at 10 years.
Ors et al.23)	Kaplan–Meier survivorship estimate with end point of revision for any reason as was 94.5% (95% CI 90.5-98.5) at 10 years.
Ozden et al.25)	With any revision as end point per log rank test 10-year survival rate of Reflection-Ceramic Interfit cup and femoral component was 97.7% (95% CI 85.4%-99.6%) and 91.0% (95% CI 78.0%-96.6%).
Reikerås et al.32)	Kaplan–Meier survivorship estimate with end point removal of component was 100% for stem and 75% for cup at 15 years.
Group 3 (n=1)
Rollo et al.26)	Survival analysis not estimated.
Total (n=20)

CI: confidence interval..

6. Radiographic Outcomes

Stable bony and fibrous ingrowth in 261 and 15 stems were recorded on follow-up radiographs. Radiographic documentation of focal and uniform radiolucent zones around the stem per Gruen was described for 28 hips. From the included studies, it was impossible to determine the number of osteolytic and aseptic loosening events responsible for revision; 57 and five stems were described as neutral, with slight varus.

7. Complications

Descriptions of the most common complications are shown in Table 1. This review included 19 early and nine late dislocations. Another 18 dislocations could not be classified based on time. Treatment for these dislocations ranged from closed/open reduction in 28 hips to revision in seven hips. In three studies 103 controlled fractures were identified in group 2^22-24). None of the stabilized fractures progressed to varus collapse. Four studies^9,16,23,29) defined nonunion according to the criteria reported by Masonis et al.⁴²⁾. The treatment of nonunion varied across studies included in this review. One case of nonunion in groups 1¹⁶⁾ and 2²⁵⁾ was treated by bone grafting with or without additional fixation; another four^24,25) nonunion procedures were treated by revision of the femoral component; one patient who showed nonunion was asymptomatic and did not receive treatment³²⁾. The sciatic and obturator nerves were paralyzed in 14 hips and one hips, respectively. Nerve palsy was entirely or partially recoverable from six months to one year after the operation in 12 hips. The included studies reported the revisions of 45 cups, 22 stems, and two liners. Six studies reported heterotopic ossification of grades I to IV^{16,22,24,25,29,31)}. However, in one case the patient was disabling enough to require excision¹³⁾.

Overall, the scores for outcome showed improvement after THA with SSDO in arthritic DDH hips. However, a similar difference in the mean improvement in functional outcomes before and after the operation was observed between modular and monoblock stems at the 5-year follow-up. The survival rate ranged from 100% to 67% at a mean follow-up of 10 and 19±7 years in the modular group, while it was 100% and 75% for a cup/stem at a mean follow-up of five and 15 years, respectively, in the monoblock group. Li et al.¹²⁾ reported an estimated mean improvement in Harris hip scores of 26.79%. Although high rates of nonunion were observed in both groups, sporadic nonunion at the SSDO site irrespective of the mode of stabilization was observed in both groups. Li et al.¹²⁾ reported no association between nonunion and subtrochanteric osteotomy designs following SSDO with THA. The pooled estimate for nonunion was 3.79% (95% CI 2.60%-5.20%) in a review of 37 studies that included 795 hips. More cases of nonunion were observed in the monoblock group; however, a conclusion of nonunion based on methodically flawed study designs and unequal cases between subgroups would be inaccurate. Three possible interventions were used in studies included in this review to address nonunion. While clinically asymptomatic cases of nonunion were left untreated, other cases were treated with stem revision rather than bone grafting and fixation. Osteointegration of the stem across the osteotomy site could be the reason for clinically asymptomatic nonunion in a few patients. Aseptic loosening, recurrent dislocations, and periprosthetic fractures were the main reasons for revision. Infection, recall of the implant, perforation, and nonunion at the osteotomy site were infrequent reasons for revision.

We expected more revisions due to the modularity of femoral stems; however, there were 7.9% and 7.4% cases of revision due to any cause at a mean follow-up of 10±4 years (range, 8-19 years) and 8.9±2.35 years (range, 5.7-13 years) for groups 1 and 2, respectively. Uncontrolled proximal and distal fractures in the dysplastic femoral canal were expected among DDH patients in both groups; however, no controlled fractures were needed in group 1 to accommodate the modular prosthesis. Given the poor quality of the studies (retrospective extended case series) included in both groups, we cannot rely on the absence of reportable varus failures with controlled and uncontrolled fractures. Augmentation of the acetabular wall from the autologous femoral head is required for many DDH patients. Published literature on the long-term benefits of autologous femoral head bulk grafts has been controversial. While Kim and Kadowaki⁴³⁾ reported a survival rate of 94% without acetabular revision for any reason at ten years, Karczewski et al.⁴⁴⁾ reported a revision rate of 8.3%, with 73% of revisions due to loosening. The need for a structural autograft can depend on the thickness of the medial wall, the size of the acetabular wall defect, and the experience of the operating surgeon. We observed that support for the cup was no longer necessary as the study investigators gained experience operating on high-riding hips. Smaller cups ranging from 40-48 mm were used by the study investigators to obtain good coverage of the acetabulum. Medial acetabular wall osteotomy was employed in two studies to reach coverage of the acetabulum^10,32). Reports on outcomes of medial acetabular wall osteotomy are limited to case series; however, excellent to good Harris hip scores were achieved at a mean follow-up of five years or more using this technique⁴⁵⁾; 22% of revisions were required for dislocations in THA⁴⁶⁾. Dislocations after hip arthroplasty can be classified based on the duration of the operation. Most cases (70%) of dislocation occur within six weeks of the operation⁴⁶⁾. A trend indicating recurrence was reported for one-third of dislocations sustained within six weeks of the operation. The reasons for dislocation after THA were classified according to surgeon, implant, and patient factors by Brooks⁴⁷⁾. Comparable rates of dislocation were observed between the groups included in this review. Sensitivity analysis was performed to examine clinical heterogeneity. Studies that included Crowe I, II, and III hips were excluded, while reports that included Crowe IV hips were included. No difference in outcome scores for function were observed between studies that included exclusive Crowe IV and all Crowe’s hips. Significant methodical heterogeneity was introduced due to the variability in reporting radiological outcomes among the included studies. The authors of that study, who used diverse criteria for assessment of osteointegration and loosening described osteointegration of the stem and cup using the Engh, DeLee, and Charnley criteria but failed to report the numbers. Although few studies have reported the statistical significance of these outcomes and survival, the clinical difference observed after cementless THA for DDH patients is significant enough.

Li et al.¹²⁾ compared union rates among various SSDO designs (transverse, chevron, and step cut) in THA among DDH hips. The authors reported that the incidence of nonunion, functional outcomes, or complications was not influenced by the osteotomy design. However, we noted extensive clinical and methodical diversity in the selection of studies by the reviewers. Factors that might have influenced outcomes in their review include the following: (1) inclusion criteria for case series with fewer than 10 patients, (2) studies using cementless, cemented, and mixed components, and (3) off-the-shelf prostheses using osteotomy was also reported 4. The reports included clinically diverse patients as well as patients who underwent Girdlestone excision arthroplasty and neglected traumatic hip dislocation. In some studies, SSDO combined with THA was not used in treatment of all included patients.

Failure to demonstrate differences in outcomes between modular and monoblock stem designs despite the use of systematic methods was the principal limitation of this review. This may be due to the absence of comparative study designs and the selective inclusion of studies with a minimum of five years of follow-up. Weak studies with significant limitations in the study design and a high risk of bias were included. Retrospective single-arm noncomparative studies can introduce significant bias. Non-Crowe III and IV patients, 1.5% of the patients, may have influenced our results. Studies that used plates with cables and locking compression plates for fixation of the osteotomy site should have been used. However, studies examining the effects of plates on fixation of the osteotomy site in hip arthroplasty among Crowe hips had a minimum follow-up period of five years^48,49). Conduct of well-designed prospective studies comparing outcomes between modular and monoblock prostheses for high-riding hips could be helpful to investigators in the effort to draw definite conclusions regarding the efficacy of monoblock and modular stem designs.

We conclude that the improvement in functional outcome between monoblock and modular stem was similar and an increased incidence of controlled fractures was observed when using monoblock stems. Nonunion at the osteotomy site can be a sporadic occurrence in patients with arthritic DDH undergoing THA using cementless stem designs. The data is inadequate to support the advantages of using cables and wires for augmenting the SSDO site.

No funding to declare.

No potential conflict of interest relevant to this article was reported.