[Advances in genetic research on Non-syndromic congenital joint synostosis].

Congenital joint synostosis (CJS) is a functional impairment resulting from failure in joint morphogenesis during embryonic development. Clinically, it may be classified as syndromic (sCJS) and non-syndromic (nsCJS) disorders. Common sCJS include chromosomal disorders such as Klinefelter syndrome and single-gene disorders like Apert/Pfeiffer/Crouzon syndromes, Holt-Oram syndrome, Ehlers-Danlos syndrome, and Radial-ulnar synostosis with thrombocytopenia, presenting with multiple system/organ anomalies. By contrast, nsCJS manifest with only joint abnormalities, affecting one or multiple joints. This review has focused on human nsCJS and its genetic etiology. To date, variants in seven genes (NOG, GDF5, FGF9, GDF6, FGF16, SMAD6, and MECOM) have been identified as causative factors for nsCJS. This review has focused on such genes and provided a comprehensive review for the clinical phenotypes, genetic patterns, common variants, and underlying mechanisms associated with nsCJS based on a literature review. In addition, it has also analyzed other candidate genes for nsCJS within the context of relevant signaling pathways involved in joint morphogenesis.

A novel variant in the FLNB gene associated with spondylocarpotarsal synostosis syndrome.

OBJECTIVES: Genetic disorders involved in skeleton system arise due to the disturbance in skeletal development, growth and homeostasis. Filamin B is an actin binding protein which is large dimeric protein which cross link actin cytoskeleton filaments into dynamic structure. A single nucleotide changes in the FLNB gene causes spondylocarpotarsal synostosis syndrome, a rare bone disorder due to which the fusion of carpels and tarsals synostosis occurred along with fused vertebrae. In the current study we investigated a family residing in north-western areas of Pakistan. METHODS: The whole exome sequencing of proband was performed followed by Sanger sequencing of all family members of the subject to validate the variant segregation within the family. Bioinformatics tools were utilized to assess the pathogenicity of the variant. RESULTS: Whole Exome Sequencing revealed a novel variant (NM_001457: c.209C>T and p.Pro70Leu) in the FLNB gene which was homozygous missense mutation in the FLNB gene. The variant was further validated and visualized by Sanger sequencing and protein structure studies respectively as mentioned before. CONCLUSIONS: The findings have highlighted the importance of the molecular diagnosis in SCT (spondylocarpotarsal synostosis syndrome) for genetic risk counselling in consanguineous families.

Posttraumatic proximal radioulnar synostosis: Current concepts on the clinical presentations, classifications, and open surgical approaches.

In the forearm, posttraumatic heterotopic ossification usually forms as a proximal radioulnar synostosis. It can occur after soft tissue injury involving the interosseous membrane or after surgery involving the radio and ulna, such as distal biceps tendon repair. It can also be induced by radial head dislocation or fracture. Screening radiography can be used to select the appropriate time for excision. The synostosis can be resected when the ectopic bone margin and trabeculation appear mature on radiographs. An interval of 6-12 months from the injury is generally recommended based on ectopic bone maturity. Selection of the surgical approach depends on site, extension (elbow joint or proximal radioulnar joint), severity of the initial articular surface, and periarticular tissue injury. The posterolateral approach is indicated for synostoses: at or distal to the bicipital tuberosity, at the level of the radial head, and proximal radioulnar joint. The posterior global approach is recommended when the forearm synostosis is associated with complete bony ankylosis of the elbow involving the distal aspect of the humerus. After surgical resection of a proximal radioulnar synostosis, the exposed bone surfaces can be covered with interposition material to minimize recurrence.

Resection Arthroplasty Is a Valuable Strategy for Humeroradial Synostosis - A Case Report.

A 15-year-old girl with humeroradial synostosis since birth underwent a resection arthroplasty. A trapezoidal resection osteotomy of approximately 2 cm was performed at the anterior part of the bone flexure. This resulted at 18 months in an elbow arc of motion of 60°-110° and forearm pronation/supination of 40° and 60° without postoperative complications and improved disabilities of the arm, shoulder and hand and Hand 20 scores. Radiographic analysis revealed a humeroradial joint with a maintained pseudarthrosis and hinged motion at the humeroulnar joint. When performed by an experienced surgeon, resection arthroplasty corrects humeroradial synostosis, resulting in improvement in range of motion and quality of life. Level of Evidence: Level V (Therapeutic).

Effects of simulated radioulnar synostosis on supination and pronation in cats. A cadaveric study.

OBJECTIVE: To evaluate the effect of an induced synostosis with a screw on pronation and supination in cats. STUDY DESIGN: Ex vivo biomechanical study. SAMPLE POPULATION: A total of 58 feline forelimbs. METHODS: A total of 58 cadaveric feline thoracic limbs were mounted on a custom-built jig with the elbow and carpus flexed at a 90° angle. To exclude any orthopedic disease, radiographs of the forelimbs were performed prior to the mechanical tests. Radioulnar synostosis was imitated with a 2 mm cortical screw through the radius into the ulna in the proximal (Group P; n = 54), middle (Group M; n = 52), and distal (Group D; n = 53) radial diaphysis. The angles of pronation and supination were recorded after manually applying a two-finger tight rotational force to the metacarpus. Rotational tests were performed without a screw (Group N) and with a screw in each of the aforementioned positions. Pairwise comparisons between the groups were performed based on their angles of rotation with a paired t-test with the Benjamini-Hochberg procedure and a mixed model ANOVA. RESULTS: Mean angles of rotation decreased between Group N (129.5 ± 15.9°) and all groups with imitated radioulnar synostosis to a mean angle of 37.5 ± 14.5° (p < .0001). Mean angles of rotation did not differ between the groups with imitated radioulnar synostosis. CONCLUSION: Induced radioulnar synostosis decreases antebrachial rotation by more than two-thirds, regardless of location. CLINICAL SIGNIFICANCE: Implants fixating the radius to the ulna should be avoided in cats, regardless where they are located along the radial diaphysis.

Raine syndrome: Prenatally identified severe craniofacial phenotype with multisuture synostosis and brain abnormalities associated with variants in FAM20C.

Raine syndrome (MIM 259775) is a rare autosomal recessive disorder, first described by Raine et al. in 1989, with an estimated prevalence of <1/1,000,000. This is due to pathogenic variants in FAM20C characterized by osteosclerosis, typical craniofacial features, and brain calcifications. Here, we report a novel variant in FAM20C, describe a uniquely severe craniofacial and CNS phenotype of Raine syndrome, and correlate it with prenatal findings. Fetal phenotyping was based on ultrasound and MRI. Solo exome sequencing was performed from DNA extracted from postmortem skin biopsy. Targeted parental variant testing was subsequently performed. A homozygous missense variant NM_020223.4 (c.1445 G > A (p.Gly482Glu)) was identified in FAM20C associated with Raine syndrome. The infant had the characteristic dysmorphic features seen in Raine syndrome. He had particularly significant CNS manifestations consisting of multisuture craniosynostosis with protrusion of the brain parenchyma through fontanelles and cranial lacunae. Histological sections of the brain showed marked periventricular gliosis with regions of infarction, hemorrhage, and cavitation with global periventricular leukomalacia. Numerous dystrophic calcifications were diffusely present. Here, we demonstrate the identification of a novel variant in FAM20C in an infant with the characteristic features seen in Raine syndrome. The patient expands the characteristic phenotype of Raine syndrome to include a uniquely severe CNS phenotype, first identified on prenatal imaging.

A novel missense mutation in the MECOM gene in a Chinese boy with radioulnar synostosis with amegakaryocytic thrombocytopenia.

Radioulnar synostosis with amegakaryocytic thrombocytopenia (RUSAT) type 2, caused by MDS1 and EVI1 complex locus (MECOM) gene mutations, is a rare inherited bone marrow failure syndrome (IBMFS) with skeletal anomalies, characterized by varying presentation of congenital thrombocytopenia (progressing to pancytopenia), bilateral proximal radioulnar synostosis, and other skeletal abnormalities. Due to limited knowledge and heterogenous manifestations, clinical diagnosis of the disease is challenging. Here we reported a novel MECOM mutation in a Chinese boy with typical clinical features for RUSAT-2. Trio-based whole exome sequencing of buccal swab revealed a novel heterozygous missense mutation in exon 11 of the MECOM gene (chr3:168818673; NM_001105078.3:c.2285G > A). The results strongly suggest that the variant was a germline mutation and disease-causing mutation. The patient received matched unrelated donor hematopoetic stem cell transplantation (HSCT). This finding was not only expanded the pathogenic mutation spectrum of MECOM gene, but also provided key information for clinical diagnosis and treatment of RUSAT-2.

Homozygous SMAD6 variants in two unrelated patients with craniosynostosis and radioulnar synostosis.

BACKGROUND: SMAD6 encodes an intracellular inhibitor of the bone morphogenetic protein (BMP) signalling pathway. Until now, rare heterozygous loss-of-function variants in SMAD6 were demonstrated to increase the risk of disparate clinical disorders including cardiovascular disease, craniosynostosis and radioulnar synostosis. Only two unrelated patients harbouring biallelic SMAD6 variants presenting a complex cardiovascular phenotype and facial dysmorphism have been described. CASES: Here, we present the first two patients with craniosynostosis harbouring homozygous SMAD6 variants. The male probands, both born to healthy consanguineous parents, were diagnosed with metopic synostosis and bilateral or unilateral radioulnar synostosis. Additionally, one proband had global developmental delay. Echocardiographic evaluation did not reveal cardiac or outflow tract abnormalities. MOLECULAR ANALYSES: The novel missense (c.[584T>G];[584T>G], p.[(Val195Gly)];[(Val195Gly)]) and missense/splice-site variant (c.[817G>A];[817G>A], r.[(817g>a,817delins[a;817+2_817+228])];[(817g>a,817delins[a;817+2_817+228])], p.[(Glu273Lys,Glu273Serfs*72)];[(Glu273Lys,Glu273Serfs*72)]) both locate in the functional MH1 domain of the protein and have not been reported in gnomAD database. Functional analyses of the variants showed reduced inhibition of BMP signalling or abnormal splicing, respectively, consistent with a hypomorphic mechanism of action. CONCLUSION: Our data expand the spectrum of variants and phenotypic spectrum associated with homozygous variants of SMAD6 to include craniosynostosis.

Imaging characteristics of too-long anterior process syndrome in children and adolescents.

BACKGROUND: In the presence of pain over the lateral aspect of the foot or recurrent ankle sprain in children, medical imaging is often employed to investigate potential causes, such as a calcaneonavicular coalition or a too-long anterior process (TLAP) of the calcaneus. Diagnosis and categorization of calcaneonavicular coalitions (synostosis, synchondrosis, or synfibrosis) is generally facilitated through imaging, in contrast to TLAP, which lacks well-defined semiological characteristics, apart from a calcaneonavicular space measurement of less than 5 mm. However, this measurement initially performed on an oblique view radiograph can be subject to a lack of precision due to positional variations of the foot and overlapping bones. Furthermore, the differentiation between TLAP as an anatomical variant and TLAP syndrome (characterized by symptomatic presentation), remains a subject of uncertainty. OBJECTIVE: The objective of our retrospective study was to investigate the imaging diagnosis of TLAP syndrome. MATERIALS AND METHODS: A retrospective unmatched case-control study was conducted, covering data from February 2014 to January 2021. All patients, included retrospectively and consecutively, were initially managed in our hospital with radiography and/or computed tomography (CT) and/or magnetic resonance imaging (MRI). Two radiologists independently reviewed the images taken (radiographs, CT scans, and MRIs) of patients undergoing treatment in pediatric orthopedics for TLAP syndrome and control subjects, utilizing a standardized questionnaire. The control group consisted of subjects with no features suggestive of TLAP syndrome. The questionnaire included measurements of the calcaneonavicular space and identification of indirect signs associated with calcaneonavicular coalitions, as described in the related literature. RESULTS: A total of 128 patients who met the inclusion criteria were included in the analysis, including 38 patients and 90 controls. The prevalence of TLAP was 71.5% in the study population and 62.6% among controls. A threshold measurement of the calcaneonavicular space at 3.2 mm favored TLAP syndrome (sensitivity=97%, specificity=70%, area under the curve [95% confidence interval] =0.881[0.812-0.949]), with better precision using CT. Three indirect signs were significant: the "anteater nose" sign, the talar beak, and the tapered anterior calcaneal process. These signs demonstrated an even stronger association with TLAP syndrome when observed in conjunction with a reduction in the calcaneonavicular space, particularly in CT scans. CONCLUSION: TLAP is common among control subjects. Therefore, a variant appears to be the most plausible explanation and it can be considered a mild form of calcaneonavicular coalition. However, in conjunction with symptoms suggestive of TLAP syndrome, the diagnosis is further supported by imaging, specifically with a calcaneonavicular space measurement of less than 3.2 mm. This measurement is most accurately obtained using CT with 2-dimensional reconstructions in all three planes. The simultaneous presence of the "anteater nose" sign, the talar beak, or the tapered anterior calcaneal process provides additional diagnostic evidence. In the diagnostic approach of calcaneonavicular coalition, oblique foot radiography seems useful in initially detecting abnormal coalition (bony or not), and complementarily, CT emerges as the best modality to characterize TLAP syndrome.

[Surgical treatment of congenital scoliosis]. / Operative Therapie der kongenitalen Skoliosen.

OBJECTIVE: Early correction of congenital scoliosis including short fusion, while minimizing both mobility restrictions and growth impairment. INDICATIONS: Congenital scoliosis with marked deformity, proven progression, significant compensatory curves, and/or impairment of trunk balance. Furthermore, in case of compression of neural structures or pain due to secondary degeneration. CONTRAINDICATIONS: No absolute contraindication. SURGICAL TECHNIQUE: Posterior approach to the apex of the deformity. In the growing spine the periosteum should only be touched at the levels where fusion is planned. Insertion of pedicle screws adjacent to the hemivertebra. The posterior elements of the hemivertebra are removed: lamina, joint facets, pedicle, transverse process. Resection of the accessory proximal rib in the thoracic spine. Following blunt dissection at the lateral and anterior surface of the hemivertebra, the body of the hemivertebra and the adjacent discs are resected. The resulting gap is closed by compression via transpedicular instrumentation thus correcting the scoliotic deformity. In case of synostosis or contralateral bar formation, the concave side of the spine is dissected and the synostosis osteomized. POSTOPERATIVE MANAGEMENT: Early mobilization on postoperative day 1. Bracing for 12 weeks depending on stability of the instrumentation. Periodic clinical and radiographic controls until the end of growth. RESULTS: Posterior hemivertebra resection with transpedicular instrumentation is considered as the standard treatment of congenital scoliosis. Correction rates of 60-80% are achieved. Cervical and lumbosacral hemivertebrae may require an additional anterior approach. In case of synostosis, bar formation, or rib synostosis, further corrective surgeries may be necessary during growth.

Raine's syndrome: rare disease from neurosurgical perspective.

Raine's syndrome (RS) is a rare genetic disorder. Only 25 cases are in literature. Occurs due to genetic mutation resulting in deranged bone metabolism. Few cases are reported discussing the neurosurgical ramifications of the disease. We report a child diagnosed with RS. He was presented with multisutural synostosis requiring craniofacial intervention with two vault expansions. Additionally, required VP shunt due to hydrocephalus. We consider our case unique among reports of RS, as our patient has survived for 10. He died due to valve obstruction of the VP shunt. We also present a review of relevant medical literature.

Presence of anomalous flexor carpi radialis brevis (FCRB) in Madelung's deformity.

An anomalous flexor carpi radialis brevis (FCRB) muscle was present in four of nine patients undergoing surgery for Madelung's deformity. This disproportionately frequent finding suggests an embryologic dysgenesis of forearm formation rather than a developmental tethering of Vicker's ligament.Level of evidence: IV (case series).

Surgical outcomes of segmental diaphyseal forearm fractures in adults: a small case series on plate osteosynthesis, intramedullary nailing, and other surgical methods.

BACKGROUND: Segmental fractures often result from high-energy or indirect trauma that causes bending or torsional forces with axial loading. We evaluated surgical outcomes of patients with forearm segmental diaphyseal fractures. METHODS: We retrospectively analyzed data from patients with forearm segmental fractures for which they underwent surgery at the Pusan National University Trauma Center from March 2013 to March 2022. We also analyzed accompanying injuries, injury severity score (ISS), injury mechanism, occurrence of open fracture, surgical technique, and treatment results. RESULTS: Fifteen patients were identified, one with bilateral segmental diaphyseal forearm bone fracture, for a total of 16 cases. Nine of the patients were male. The overall mean age was 50 years, and the mean follow-up period was 16.2 months. Six cases who underwent surgery using plate osteosynthesis achieved bone union without length deformity at final follow-up. Three of seven patients who underwent intramedullary nailing alone underwent reoperation due to nonunion. Six cases achieved bone union at final follow-up, three of which showed length deformity. Three patients underwent surgery using a hybrid method of IM nailing, plates, and mini cables. One patient who underwent surgery with a plate and one patient who underwent surgery with IM nailing alone showed nonunion and were lost to follow-up. CONCLUSION: Plate osteosynthesis is considered the gold standard for treatment of adult forearm diaphyseal segmental fractures. In this study, IM nailing was associated with high rates of non-union and length deformity. However, the combination of IM nailing and a plate-cable system may be an acceptable alternative in segmental diaphyseal forearm fracture, achieving a union rate similar to that provided by plate fixation.

A variant in the LDL receptor-related protein encoding gene LRP4 underlying polydactyly and phalangeal synostosis in a family of Pakistani origin.

A family of Pakistani origin, segregating polydactyly, and phalangeal synostosis in an autosomal dominant manner, has been investigated and presented in the present report. Whole-exome sequencing (WES), followed by segregation analysis using Sanger sequencing, revealed a heterozygous missense variant [c.G1696A, p.(Gly566Ser)] in the LRP4 gene located on human chromosome 11p11.2. Homology protein modeling revealed the mutant Ser566 generated new interactions with at least four other amino acids and disrupted protein folding and function. Our findings demonstrated the first direct evidence of involvement of LRP4 in causing polydactyly and phalangeal synostosis in the same family. This study highlighted the importance of inclusion of LRP4 gene in screening individuals presenting polydactyly in hands and feet, and phalangeal synostosis in the same family.

[Analysis of phenotype and pathogenic variants in a Chinese pedigree affected with Multiple synostoses syndrome type 1].

OBJECTIVE: To explore the clinical and genetic characteristics of a Chinese pedigree affected with Multiple synostoses syndrome type 1 (SYNS1). METHODS: Clinical data of the proband and her family members were collected. Genomic DNA was extracted from peripheral blood samples. Whole-exome sequencing (WES) and whole-genome sequencing (WGS) were carried out for the proband and her parents. RESULTS: The pedigree has comprised of 14 members from three generations, of whom six had manifested hearing loss, with other symptoms including proximal symphalangism, hemicylindrical nose, amblyopia, strabismus, brachydactyly, incomplete syndactyly, which fulfilled the diagnostic criteria for SYNS1. WES had detected no pathogenic single nucleotide variants and insertion-deletion (InDel) in the coding region of the NOG gene, whilst copy number variation (CNV) analysis indicated that there was a heterozygous deletion involving the NOG gene. WGS revealed a heterozygous deletion (54171786_55143998) in 17q22 of the proband. The CNV was classified as pathogenic based on the guidelines from the American College of Medical Genetics and Genomics (ACMG). CONCLUSION: The heterozygous deletion in 17p22 involving the NOG gene probably underlay the pathogenesis of SYNS1 in this pedigree. Above finding has enriched the mutational spectrum of NOG. CNV should be considered when conventional sequencing has failed to detect any pathogenic variants in such patients.

Outcomes of surgical management for tarsal coalitions: a systematic review.

PURPOSE: To analyze the outcome of surgical treatment of tarsal coalition, assess the role of the surgical technique, as well as of coalition size and type on outcomes. METHODS: The search followed the Preferred Reporting Items of Systematic Review and Meta-Analysis and was performed in four databases: MEDLINE, Central, Scopus and Web of Science. The protocol has been registered in the international prospective register of systematic reviews. Patient-reported outcomes (PROMs), complications, revisions and radiographic recurrence were collected. Risk of bias was assessed using MINORS criteria. A random-effects model for meta-analysis was applied for analysis of data heterogeneity. RESULTS: Twenty-five studies including 760 tarsal coalitions were included and had a weighted average follow-up of 44 months. Studies scored fair to poor on the risk of bias assessment with a mean MINORS score of 67% (44-81%). In 77.8% (37.5-100%) of surgically treated tarsal coalitions, good/excellent/non-limiting or improved PROMs were reported. Calculated data heterogeneity was moderate (I2 = 57%). Open bar resection with material interposition had a clinical success rate of 78.8% (50-100%). Complications occurred in 4.96% of cases. Coalition size did not prove to be a determining factor in postoperative outcome. The influence of the coalition type was not investigated by any of the studies. CONCLUSION: Data on outcomes of surgical management for tarsal coalitions is limited to retrospective case series with high risk of bias and moderate data heterogeneity. In about ¾ of cases, open resection and interposition of material results in improved PROMs. The arbitrary margin of ≥ 50% of TC coalition size in relation to the posterior facet has little importance in surgical decision-making. None of the studies reported on the influence of the coalition type on postoperative clinical success.

A De Novo 8q22.2q22.3 Interstitial Microdeletion in a Girl with Developmental Delay and Congenital Defects.

Background and Objectives: Only nine patients with interstitial de novo 8q22.2q22.3 microdeletions have been reported to date. The objective of this report is to present clinical features of a new patient with an 8q22.2q22.3 microdeletion, to compare her phenotype to other previously reported patients, and to further expand the phenotype associated with this microdeletion. Materials and Methods: We describe an 8½-year-old girl with developmental delay, congenital hip dysplasia, a bilateral foot deformity, bilateral congenital radioulnar synostosis, a congenital heart defect, and minor facial anomalies. Results: Chromosomal microarray analysis revealed a 4.9 Mb deletion in the 8q22.2q22.3 region. De novo origin was confirmed by real-time PCR analysis. Conclusions: Microdeletions in the 8q22.2q22.3 region are characterized by moderate to severe intellectual disability, seizures, distinct facial features and skeletal abnormalities. In addition to one already reported individual with an 8q22.2q22.3 microdeletion and unilateral radioulnar synostosis, this report of a child with bilateral radioulnar synostosis provides additional evidence, that radioulnar synostosis is not an incidental finding in individuals with an 8q22.2q22.3 microdeletion. Additional patients with similar microdeletions would be of a great importance for more accurate phenotypic description and further analysis of the genotypic-phenotypic relationship.

Clavicular bone defects managed with free vascularised fibular grafting: evidence to date.

Reconstructive surgery of the clavicle using free vascularised fibula grafting (FVFG) is sometimes required for the management of severe bone loss or non-union. As the procedure is relatively rare, there is no universal agreement on the management and outcome. This systematic review aimed to first, identify the conditions for which FVFG has been applied; second, to gain an understanding of the surgical techniques used; and third, to report outcomes related to bone union, infection eradication, function and complications. A PRISMA strategy was used. Medline, Cochrane Central Register of Controlled Trials, Scopus and EMBASE library databases were interrogated using pre-defined MeSH terms and Boolean operators. Quality of evidence was evaluated based on OCEBM and GRADE systems. Fourteen studies based on 37 patients were identified with a mean follow-up time of 33.3 months. The most common reasons for the procedure were: fracture non-union; tumours requiring resection; post-radiation treatment osteonecrosis and osteomyelitis. The operation approaches were similar, involving graft retrieval, insertion and fixation and vessels chosen for reattachment. The mean clavicular bone defect size was 6.6 cm (± 1.5), prior to FVFG. Bone union occurred in 94.6% with good functional outcomes. Complete infection eradication occurred in those with preceding osteomyelitis. The main complications were broken metalwork, delayed union/non-union and fibular leg paraesthesia (n = 20). The mean re-operation number was 1.6 (range 0-5.0). The study demonstrates that FVFG is well tolerated and has a high success rate. However, patients should be advised about complication development and re-intervention requirement. Interestingly, overall data is sparse with no large cohort groups or randomised trials.

Three-dimensional femur morphology analysis for the optimal location of subtrochanteric osteotomy with an implanted Wagner cone stem in total hip arthroplasty for Crowe type IV developmental dysplasia of the hip.

BACKGROUND: This study aimed to accurately evaluate the matching of proximal and distal femoral segments and fitting of the femur-femoral stem in patients with Crowe type IV developmental dysplasia of the hip (DDH) who have undergone subtrochanteric osteotomy at different locations with an implanted Wagner cone stem to improve the rate of the bone union at the osteotomy site. METHODS: Three-dimensional femur morphology of 40 patients with Crowe type IV DDH was evaluated at each cross-section to determine the femoral cortical bone area. This study focused on five osteotomy lengths (2.5, 3, 3.5, 4, and 4.5 cm). The overlapped area between the proximal and distal cortical bone segments was defined as the contact area (S, mm2), and the contact area to distal cortical bone area ratio was defined as the coincidence rate (R). Three indicators were used to evaluate the matching and fitting of the osteotomy sites with the implanted Wagner cone stems: (1) higher S and R between the proximal and distal segments; (2) the effective fixation length of the femoral stem at the distal segments being at least 1.5 cm; and (3) osteotomy did not involve the isthmus. RESULTS: In all groups, S significantly decreased in the two proximal levels above the 0.5 cm level below the lesser trochanter (LT) compared with those below this level. In comparison, at osteotomy lengths from 2.5 to 4 cm, R significantly decreased in the three proximal levels. The optimal osteotomy levels ranged from 1.5 and 2.5 cm below the LT for an appropriately sized stem. CONCLUSIONS: Subtrochanteric osteotomy at the optimal level not only ensures fitting of the femur-femoral stem but also meets the requirements of a higher S and R to ensure adequate reduction and stabilization at the osteotomy site, which may contribute to the bone union. Although the optimal osteotomy level varies with the size of the femoral stem and the length of the subtrochanteric osteotomy, the optimal osteotomy levels for an appropriately sized Wagner cone femoral stem implantation range from 1.5 to 2.5 cm below the LT.