Does retrograde entry in femoral lengthening over nail allow greater lengthening without increasing complications? A single-surgeon cohort study

Abstract

Background

Despite advances in motorized internal lengthening nails, the lengthening over an intramedullary nail (LON) technique remains relevant in selected clinical scenarios. In femoral LON, both antegrade and retrograde nailing directions may be considered according to osteotomy level, deformity characteristics, and planned lengthening. Although antegrade entry is more commonly preferred, retrograde entry may offer technical advantages in selected cases. This study compared outcomes and complications between antegrade and retrograde femoral LON in a single-surgeon cohort.

Methods

A retrospective cohort of 44 femoral lengthening procedures between 1997 and 2018 was analyzed. Patients were divided into antegrade (n = 18) and retrograde (n = 26) groups based on nail entry direction. Demographic characteristics, lengthening parameters, consolidation indices, callus quality, outcome scores, and complications, which were classified using a standardized system, were compared between groups. Statistical significance was set at p < 0.05.

Results

The mean lengthening amount and percentage were higher in the retrograde group. The consolidation index and regenerate quality were comparable between groups. No statistically significant difference was observed between groups in overall complication rates or Grade 3 complications. Outcome scores were significantly higher in the antegrade group. Difficulty level was positively correlated with Grade 3 complications and poor callus quality.

Conclusions

In this retrospective single-surgeon cohort, retrograde entry in femoral LON was associated with a higher amount of achieved lengthening and percentage compared with antegrade entry, without an observed increase in overall complication rates. However, these findings should not be interpreted as evidence that retrograde entry independently permits greater lengthening or carries no additional risk, because entry direction was likely influenced by preoperative case selection, planned lengthening amount, osteotomy location, deformity characteristics, and surgeon-specific decision-making. Retrograde entry may be considered a viable option in carefully selected femoral LON cases, but larger prospective studies are needed to clarify its indications, complication profile, and comparative effectiveness.

Keywords

lengthening over intramedullary nailing limb lengthening LON comparison complications nail direction

Introduction

The advent of distraction osteogenesis revolutionized the field of limb lengthening, leading to the development of several techniques aimed at improving patient comfort, reducing external fixation-related morbidity, and minimizing complication rates.^1,2 Among these developments, motorized intramedullary lengthening nails represent the most recent stage in the transition from external or hybrid fixation methods toward fully internal lengthening systems. These implants were developed after the introduction of the lengthening over an intramedullary nail (LON) technique and were designed to reduce transfixation-related complications and improve functional recovery during limb lengthening procedures.^3,4

Although motorized internal lengthening nails represent a major advancement, their application may still be limited in certain clinical scenarios. Current implant designs may restrict early or full weight-bearing during regenerate formation, which can be important for promoting regenerate maturation. In addition, distraction capacity may be insufficient in short nails, mismatch between intramedullary canal diameter and patient weight may limit implant selection, multiple osteotomies may be required in complex deformities, and cost or accessibility may remain important barriers.^5–7 In such situations, the LON technique may still offer practical advantages. Conventional intramedullary nails used in LON can provide a more robust internal support after distraction, while the external fixator allows gradual lengthening and, when necessary, control of multiple bone segments through additional fixation elements. Therefore, the persistence of LON in contemporary practice cannot be explained solely by cost; rather, it reflects a combination of biological, mechanical, technical, and practical considerations.^8,9

In the traditional LON procedure for femoral lengthening, the piriformis fossa or the tip of the greater trochanter may serve as the entry point for antegrade femoral nailing, whereas the intercondylar notch is used for retrograde nailing; a unilateral external fixator is then employed for distraction osteogenesis. Although both antegrade and retrograde nailing techniques have their respective advantages, antegrade nailing may be favored in the LON technique because it avoids intra-articular entry and potential risks to the extensor mechanism and knee joint. It is therefore commonly selected unless specific clinical indications require a retrograde approach.^8,10

However, retrograde nailing may provide certain advantages in selected femoral lengthening scenarios. The osteotomy level associated with retrograde femoral nailing is often closer to the metaphyseal or metadiaphyseal region, where a broader bone surface and richer vascularity may support more reliable regenerate formation and potentially allow greater distraction. This may be particularly relevant in cases involving bone defects or nonunion. Furthermore, the anatomy of the distal femur may facilitate simultaneous deformity correction and intramedullary nailing, especially when sagittal or coronal plane deformities are present. The proximity of the osteotomy to the knee joint and the functional axis of knee motion may also allow correction of sagittal plane angulation, flexion contracture, or fixed soft-tissue deformity in selected cases, such as patients with achondroplasia or complex femoral deformities. Conversely, antegrade femoral lengthening follows the anatomical axis more closely, which may limit the ability to correct or prevent valgus deviation predicted during reverse planning in some cases. Therefore, the choice of nail entry direction in femoral LON should not be regarded as a minor technical preference but as an important component of preoperative planning.

Therefore, the present study aimed to compare the outcomes and complications of femoral LON procedures performed using antegrade and retrograde intramedullary nail entry directions. To our knowledge, this is the first study to directly compare both nail entry directions in classical femoral lengthening over an intramedullary nail procedures. By addressing this question, we aim to provide clinically relevant insights that may help optimize decision-making in femoral lengthening surgery.

Materials and methods

This study was approved by the Institutional Review Board of the conducting department of Istanbul University (approval date and number: 2017/09-06) and was conducted in accordance with the principles of the World Medical Association Declaration of Helsinki. It is a retrospective investigation comparing two patient groups treated with different nail directions for femoral limb lengthening over nail (LON). Due to the design and allowance of the study, informed patient consent was waived.

Patient selection

Skeletally mature patients with clinically significant femoral limb-length discrepancy or short stature who underwent femoral lengthening over an intramedullary nail with either antegrade or retrograde nailing between September 1997 and July 2018 were eligible for this study. Inclusion criteria were as follows: (1) acquired limb shortening due to post-traumatic, post-infectious, or post-physial arrest, (2) congenital short femur without joint instability, (3) syndromic conditions, including hemihypertrophy and achondroplasia, and (4) cosmetic lengthening for short stature. The exclusion criteria were as follows: (1) deformity correction exceeding 10° in any plane, (2) concomitant tibial lengthening, (3) sequela of poliomyelitis, (4) congenital or neuromuscular disorders with or without limb agenesis, (5) prior radiotherapy involving the affected extremity, (6) lengthening requiring more than one osteotomy, (7) segmental bone transport; and (8) lengthening over a prexisting intramedullary nail.

A total of 44 lengthening procedures of thirty-seven patients met these criteria. In cases of bilateral lengthening, each segment was considered a separate procedure. All complications and lengthening parameters were recorded and analyzed at the segment level. All included patients had complete data and follow-up. The choice between antegrade and retrograde techniques was based on surgeon preference and intraoperative planning, primarily considering the planned lengthening amount and optimal osteotomy location; therefore, potential selection bias cannot be excluded. Based on the nailing direction, cases were divided into two groups: antegrade nailing (Group A) and retrograde nailing (Group R). All antegrade lengthenings were unilateral, whereas seven bilateral lengthenings were present in the retrograde group. (Table1)

Table 1.

Descriptive statistics of the study groups.

		Group A (n = 18)	Group R (n = 26)	P value
Sex	Male	11 (61.1)	16 (63.2)**	^a0.898
Sex	Female	7 (38.9)	10 (36.8)**	^a0.898
Age of operation	Mean ± Sd	22.33 ± 8.13	27.89 ± 10.10	^b0.081
Age of operation	Min-Max	19 (16–49)	27 (15–47)	^b0.081
Side	Right	9 (50.0)	14 (53.8)	^a0.802
Side	Left	9 (50.0)	12 (46.2)	^a0.802
Etiology	Acquired	13 (72.2)	9 (34.6)	^c0.015^*
	Congenital	5 (27.8)	7 (26.9)
	Syndromic	0 (0)	6 (23.1)
	Cosmetic	0 (0)	4 (15.4)

Statistically significant results are marked with *p < 0.05.

**Three female, four male patients were undergone bilateral femoral lengthening.

^aPearson Chi-Square Test,

^bMann-Whitney U Test,

^cFisher-Freeman-Halton Test.

Surgical technique

All surgical procedures were performed by the senior author using the previously described technique, which was adapted based on the nailing direction.^3,11 All osteotomies were performed using multiple drilling techniques and conformed intraoperatively under fluoroscopy. A reconstruction-type femoral nail was used in all antegrade approaches, and a conventional interlocking tibial trauma nail was used in all retrograde approaches. (Figure 1) The medullary canal was overreamed by 1 mm larger than the nail. Osteotomy levels were a subtrochanteric area for antegrade nails and a distal metaphyseal-diaphyseal junction for retrograde nailing. The iliotibial band was released in all cases. Blocking screws were used to prevent excessive deviations.¹² A unilateral dynamic axial fixator was applied laterally for distraction. The targeted distraction rate of 1 mm per day was divided into four times (0.25 mm x 4 per/day), but case-dependent adjustments were made by the surgeon based on clinical and radiographic evaluation. The intramedullary nail was locked, and the fixator was removed once the desired length and alignment were achieved. In one patient, the fixator was kept until satisfactory consolidation was achieved due to insufficient callus formation.

Figure 1.

(A) Radiographic image of the left femur of a nineteen-year-old patient. A monorail external fixator with an intramedullary nail was applied in a retrograde fashion. Distal diaphyseal osteotomy was performed. The proximal end of the nail was extruded through the piriform fossa due to preoperative nail measurements, considering the final length of the femur. (B) Orthoroentgenogram of the patient during the distraction period. The nail was retracted with the distraction through the piriform fossa. (C and D) Anteroposterior and lateral radiographic images of the left femur show adequate callus formation in the distraction gap. (E and F) Radiographic images of the left femur after complete consolidation of the distraction gap. (G) The patient’s orthoroentgenogram showed a level pelvis without a discrepancy in limb length. (H and I) Clinical images of the patient showing functional results.

Follow-up and postoperative rehabilitation

Postoperative analgesia was provided by means of an epidural catheter in all patients. Full range of motion of the knee and walking with full weight bearing using two crutches were initiated on the first postoperative day. All patients were started on physical therapy by a physical therapist experienced in orthopedic rehabilitation. After removing the fixator and locking the intramedullary nail, patients were allowed toe-touch walking with two crouches. A unilateral fixator was maintained after interlocking the nail for insufficient callus formation in one case. Weight-bearing was adjusted depending on the regenerate maturity observed on the follow-up radiographs. Full weight-bearing was encouraged after the regeneration of at least three cortices was seen on the radiographs. All patients were followed every two weeks during the distraction period and monthly after external fixator removal. The minimum follow-up duration was 5 years.

Radiographic evaluation and lengthening parameters

The callus formation was classified according to the classification of Li et al., fusiform, cylindrical, concave, or laterally at the end of the distraction period in each case.¹³ The fusiform and cylindrical shapes were defined as having better callus quality than the concave and lateral shapes.¹⁴ The level of difficulty was classified according to the system described by Dror Paley and John E. Herzenberg, which considers factors such as deformity complexity, soft tissue condition, joint stability, bone quality, prior surgical interventions, and medical comorbidities. Complications were categorized according to Paley’s classification as problems (resolved without surgery), obstacles (requiring additional intervention), and true complications (permanent or unresolved issues). Outcome scores were calculated using the scoring system for femoral lengthening outcomes described in the original publication.^3,15 This system includes both additive positive criteria and subtractive negative criteria. Positive points are assigned based on knee range of motion, the amount of achieved lengthening, gait assessment at follow-up, and the final lateral distal femoral angle. Negative points are subtracted for pain and limitations in activities of daily living or work capacity. The final score is interpreted in four categories: excellent, 95–100 points; good, 75–94 points; fair, 40–74 points; and poor, less than 40 points. Accordingly, excellent and good results were considered favorable outcomes, whereas fair and poor results were considered less favorable or unfavorable outcomes.

Lengthening parameters of external fixator duration, gained femoral length, external fixator index, consolidation period, consolidation index, lengthening percentage, and mechanical axis deviation were calculated based on the literature.^3,5

Analysis of the data

The groups were compared by level of difficulty, external fixator duration, gained femoral length, external fixator index, consolidation period, consolidation index, lengthening percentage, mechanical axis deviation, callus shape and quality, complications, outcome scores, and classifications (Table 2). SPSS v.28.0.1.0 (IBM, USA) was used for statistical analysis. Descriptive statistical methods (mean, standard deviation, minimum, maximum) were used to evaluate the study data. The conformity of the quantitative data to the normal distribution was tested with the Shapiro-Wilk test and graphical examinations. The independent group’s t-test was used to compare two groups of normally distributed quantitative variables, and the Mann-Whitney U test was used to compare two groups of non-normally distributed quantitative variables. Pearson chi-square test, Fisher’s exact test, and Fisher-Freeman-Halton exact test were used to compare qualitative data. Spearman correlation analysis was used to evaluate the relationships between quantitative variables. Diagnostic screening tests (sensitivity, specificity, PPV, NPV) and ROC analysis were used to determine the cutoff value for the parameters. Statistical significance was accepted as p < 0.05.¹⁶

Table 2.

Comparison of lengthening parameters and callus quality between groups.

		Group A (n = 18)	Group R (n = 26)	P value
Level of Difficulty⁺⁺	Mild	18 (100)	21 (80.8)	^a0.068
Level of Difficulty⁺⁺	Moderate	0 (0)	5 (19.2)	^a0.068
External fixator duration (days)	Mean ± Sd	77.89 ± 32.06	98.29 ± 29.04	^b0.079
External fixator duration (days)	Min-Max	25–161	70–176	^b0.079
Length gained (millimeters)	Mean ± Sd	42.06 ± 14.09	68.29 ± 19.26	^b0.001^**
Length gained (millimeters)	Min-Max	20–80	30–100	^b0.001^**
External fixator index (days/centimeters)	Mean ± Sd	18.32 ± 4.40	15.06 ± 4.20	^c0.019^*
External fixator index (days/centimeters)	Min-Max	11.5–26.8	10.4–23.3	^c0.019^*
Consolidation period (days)	Mean ± Sd	90.28 ± 31.19	138.25 ± 53.00	^b0.005^**
Consolidation period (days)	Min-Max	26–145	39–199	^b0.005^**
Consolidation index (days/centimeters)	Mean ± Sd	22.24 ± 8.12	21.01 ± 8.66	^b0.980
Consolidation index (days/centimeters)	Min-Max	13–42.7	8.8–46	^b0.980
Lengthening percentage	Mean ± Sd	10.03 ± 3.63	18.93 ± 6.82	^b0.001^**
Lengthening percentage	Min-Max	5.2–19.5	7.1–31	^b0.001^**
Mechanical axis deviation (milimeters)	Mean ± Sd	4.00 ± 7.90	4.75 ± 7.28	^b0.908
Mechanical axis deviation (milimeters)	Min-Max	5 (-8-21)	4 (-10-20)	^b0.908
Callus Shape⁺	Fusiform	11 (61.1)	17 (70.8)	^d0.363
	Cylindrical	4 (22.2)	2 (8.3)
	Concave	1 (5.6)	4 (16.7)
	Lateral	2 (11.1)	1 (4.2)
Callus Quality⁺	Good	15 (83.3)	19 (79.2)	^a1.000
Callus Quality⁺	Poor	3 (16.7)	5 (20.8)	^a1.000

⁺Lee et al.’s classification system was used to evaluate callus shape and quality.¹³

⁺⁺Lengthening parameters of one patient with bilateral lengthening in Group R were excluded because of implant failure, nail removal, and subsequent change in treatment method. Mechanical axis deviation; negative values indicate lateral deviation and positive values indicate medial deviation, in millimeters.

^aFisher’s exact Test,

^bMann-Whitney U Test,

^cStudent’s t-test. Statistically significant results are marked with *p < 0.05 **p < 0.01.

^dFisher-Freeman-Halton Test.

A post hoc sensitivity analysis was performed to quantify the detectable between-group effect size given the available sample. With Group A (n = 18) and Group R (n = 26), a two-sided α = 0.05, the study had 80% power to detect a standardized mean difference of Cohen’s d≈0.88 (large effect) for continuous outcomes. Therefore, smaller between-group differences may not have been detected, and the analyses should be interpreted as exploratory.

Results

General demographics of both groups are presented in Table 1. The majority of cases in both groups were post-traumatic. Congenital cases were limited to isolated congenital short femur without associated deficiencies or instability. All syndromic cases consisted of achondroplasia. The mean planned lengthening was 42.06 ± 14.09 mm in the antegrade group and 68.29 ± 19.26 mm in the retrograde group, as detailed in Table 2. The desired length was achieved without changing the treatment technique in all but two procedures. One achondroplasia patient had a bilateral retrograde lengthening developed nail impingement with Schanz screw failure on the right side and premature consolidation on the left side during the distraction period. Intramedullary nails were extracted on both sides, and treatment was completed with unilateral fixator lengthening. The lengthening parameters for this patient were excluded from the results in Table 2 except the level of difficulty row, since the intramedullary nail was removed. In thirteen patients, concomitant deformity correction under 10° on the coronal and oblique planes is performed acutely with the use of a monoliteral fixator. None of these cases has undergone correction of sagittal plane or rotational deformity.

The level of difficulty, external fixator duration, length gained, external fixator index, consolidation period, consolidation index, lengthening percentage, change in mechanical axis deviation, callus patterns, and regenerate quality were shown in both groups in Table 2. The length gained, consolidation period, and lengthening percentage were significantly higher in group R, while the external fixator index was significantly higher in group A. The remaining parameters in Table 2 were statistically similar between the two groups. (p > 0.05)

Complications identified based on the published classification system are summarized in Table 3. None of the complications were statistically different between the groups. A comparison of the outcome scores is shown in Table 4. The significant correlations among the parameters were positive correlations between Level of Difficulty vs Grade 3 Complications and Poor Callus Quality, respectively (p = 0.034 and p = 0.036, p < 0.05). Regression analysis also shows that the Difficulty rate affects Total Grade 3 complications, with an effect size of 10.4% (R2 = 0.104).

Table 3.

Comparison of complications between antegrade (group A) and retrograde (group R) approaches.

		Group A (n = 18)	Group R (n = 26)	P value
		Grade 1 complications (problems)		n (%)
Contracture of the knee joint	No	7 (38.9)	6 (25.0)	^a0.335
Contracture of the knee joint	Yes	11 (61.1)	18 (75.0)	^a0.335
Delayed consolidation	No	16 (88.9)	19 (79.2)	^b0.679
Delayed consolidation	Yes	2 (11.1)	5 (20.8)	^b0.679
Decreased range of motion of the hip joint	No	15 (83.3)	23 (95.8)	^b0.297
Decreased range of motion of the hip joint	Yes	3 (16.7)	1 (4.2)	^b0.297
Superficial pin tract infection (per patient)	No	13 (72.2)	17 (70.8)	^a0.921
Superficial pin tract infection (per patient)	Yes	5 (27.8)	7 (29.2)	^a0.921
Interlocking screw fail without shortening of the regenerate	No	17 (94.4)	24 (100)	^b0.429
	Yes	1 (5.6)	0 (0)	^b0.429
Heterotopic ossification	No	17 (94.4)	23 (95.8)	^b1.000
Heterotopic ossification	Yes	1 (5.6)	1 (4.2)	^b1.000
Knee joint synovitis	No	18 (100)	23 (95.8)	^b1.000
Knee joint synovitis	Yes	0 (0)	1 (4.2)	^b1.000
Total grade 1 complications rate	Mean±Sd	1.28 ± 0.89	1.38 ± 0.82	^c0.642
Total grade 1 complications rate	Min-Max	1 (0–3)	1 (0–3)	^c0.642
Grade 2 complications (obstacles)		n (%)
Early consolidation	No	17 (94.4)	24 (100)	^b0.429
Early consolidation	Yes	1 (5.6)	0 (0)	^b0.429
Insufficient callus requiring bone grafting	No	18 (100)	23 (95.8)	^b1.000
Insufficient callus requiring bone grafting	Yes	0 (0)	1 (4.2)	^b1.000
Hip joint contracture	No	18 (100)	19 (79.2)	^b0.060
Hip joint contracture	Yes	0 (0)	5 (20.8)	^b0.060
Knee joint contracture	No	18 (100)	21 (87.5)	^b0.247
Knee joint contracture	Yes	0 (0)	3 (12.5)	^b0.247
Total grade 2 complications rate	Mean±Sd	0.06 ± 0.24	0.38 ± 0.71	^c0.088
Total grade 2 complications rate	Min-Max	0 (0-1)	0 (0-2)	^c0.088
Grade 3 complications (true complications)		n (%)
Trendelenburg gait	No	17 (94.4)	24 (100)	^b0.429
Trendelenburg gait	Yes	1 (5.6)	0 (0)	^b0.429
Interlocking screw breakage with regenerate shortening	No	17 (94.4)	24 (100)	^b0.429
Interlocking screw breakage with regenerate shortening	Yes	1 (5.6)	0 (0)	^b0.429
Intramedullary nail breakage	No	18 (100)	23 (95.8)	^b1.000
Intramedullary nail breakage	Yes	0 (0)	1 (4.2)	^b1.000
Implant failure*	No	18 (100)	24 (92.3)	^b0.505
Implant failure*	Yes	0 (0)	2 (7.7)*	^b0.505
Total grade 3 complications rate	Mean ± Sd	0.11 ± 0.32	0.12 ± 0.33	^c0.965
Total grade 3 complications rate	Min-Max	0 (0-1)	0 (0-1)	^c0.965
Total difficulty rate	Mean ± Sd	0.48 ± 0.33	0.60 ± 0.22	^c0.093
Total difficulty rate	Min-Max	0.3 (0–1.3)	0.7 (0.3–1)	^c0.093

*One patient with bilateral lengthening in Group R had implant failure requiring nail removal and a change in treatment method. This patient was excluded from the remaining statistical analyses and was included only in the implant failure row for the corresponding comparison.

^aPearson Chi-Square Test,

^bFisher’s exact test.

^cMann-Whitney U Test.

Table 4.

Comparison of outcome scores between antegrade (group A) and retrograde (group R) approaches.

		Group A (n = 18)	Group R (n = 26)	P value*
Outcome score**	Mean±Sd	93.33 ± 9.70	86.88 ± 12.05	^a0.019^*
Outcome score**	Min-Max	95 (65–100)	90 (55–100)	^a0.019^*
Outcome**	Excellent	12 (66.7)	7 (29.2)	^b0.038^*
	Good	5 (27.8)	15 (62.5)
	Fair	1 (5.6)	2 (8.3)
	Poor	0	0

*p < 0.05.

**Outcome scoring and classification was based on Paley et al.’s outcome scoring system based on clinical and radiographic criteria^3,15.

^aMann-Whitney U Test,

^bFisher Freeman Halton Test,

Discussion

The present study was conducted to compare the outcomes of femoral lengthening over an intramedullary nail performed with antegrade and retrograde nail entry directions in a single-surgeon cohort. The main finding was that retrograde entry was associated with greater achieved lengthening amount and percentage, while no statistically significant increase in complication rates or unfavorable outcome scores was observed. However, these findings should be interpreted cautiously. In particular, the greater lengthening observed in the retrograde group should not be interpreted as evidence that retrograde entry independently permits greater lengthening. Rather, it may reflect preoperative case selection, surgical planning, osteotomy location, deformity characteristics, and surgeon-specific decision-making.

Although motorized internal lengthening nails represent an important advancement in distraction osteogenesis, the LON technique may still remain relevant in selected clinical situations.^10,14,17 The limiation of the distraction capacity in short nails, mismatch between canal diameter and patient weight, restriction of early weight-bearing and promotion of regenerate formation, need for multiple osteotomies and simultaneous major deformity corrections and cost or accessibility concerns could be stated as these situations limits the use of motorized nails.^5,6,18 Additionally, LON allows gradual distraction using an external fixator while maintaining internal support with a conventional intramedullary nail after distraction.^3,8,11 Therefore, the continued use of LON technique should not be explained only by cost; it may also reflect biological, mechanical, and technical considerations in selected patients.

Within the LON technique, the choice between antegrade and retrograde femoral nailing is not a minor technical preference.^8,19 Antegrade nailing avoids intra-articular knee entry and may reduce the potential risk to the extensor mechanism and knee joint. It may also provide easier nail coverage in a narrower diaphyseal segment and may reduce the need for additional blocking screws in selected cases.¹² For these reasons, antegrade entry is often considered the preferred approach unless specific clinical or anatomical factors favor retrograde nailing.^3,8,11,14

Retrograde entry, on the other hand, may offer potential advantages in selected femoral lengthening scenarios. It may allow a closer osteotomy to the metaphyseal or metadiaphyseal region, where a broader bone surface and richer vascularity may support regenerate formation.^9,20 This biological environment may be particularly relevant in cases requiring greater distraction or in patients in whom regenerate maturation is a major concern. Retrograde entry may also facilitate simultaneous correction of distal femoral deformities and may be useful when sagittal or coronal plane correction is needed around the knee.^9,12 In addition, proximity to the knee joint may allow management of associated contractures or fixed soft-tissue deformities when required.

However, these potential advantages must be interpreted in light of selection bias. In this retrospective cohort, the decision to use antegrade or retrograde entry was not randomized. The choice of entry direction was made by the senior author according to the clinical judgment, patient anatomy, diagnosis, planned amount of lengthening, deformity characteristics, osteotomy level, and anticipated final nail position. Therefore, the greater achieved lengthening in the retrograde group may reflect the fact that retrograde entry was preferentially selected for cases in which greater lengthening or distal femoral planning was already intended. For this reason, the results of this study demonstrate an association between retrograde entry and greater achieved lengthening, but they do not establish a causal relationship.

In the present cohort, callus quality and consolidation index were comparable between groups. This suggests that, within the limits of the study, the greater mean lengthening observed in the retrograde group was not accompanied by an obvious deterioration in regenerate quality or consolidation efficiency. Nevertheless, this finding should also be interpreted cautiously. The biological advantage of a metaphyseal or metadiaphyseal osteotomy is a plausible explanation, but the retrospective design of the study does not allow this mechanism to be confirmed.^1,2 Other factors, including patient selection, surgical planning, rehabilitation compliance, and postoperative weight-bearing, may also have contributed to the observed results.

The complication findings should also be interpreted with caution. Although no statistically significant difference in overall complication rates was observed between the antegrade and retrograde groups, this should not be considered as proof that retrograde entry carries no increased risk. The cohort size was limited, and some complication events were relatively uncommon. Additionally, the study may be underpowered to detect clinically relevant differences in specific complications. In this context, the absence of statistical significance should not be equated with equivalence or safety superiority. Rather, the findings indicate that, in this single-surgeon cohort, no clear increase in complication rates was observed among patients treated with retrograde entry.

Retrograde femoral nailing requires intra-articular knee entry and therefore carries potential risks related to the knee joint, extensor mechanism, and intra-articular structures.¹⁷ For this reason, meticulous surgical technique and careful soft-tissue handling are essential. In this cohort, knee joint contracture was observed in both groups, but all contractures resolved by the end of treatment and were not considered major or true complications. The occurrence of both hip and knee contractures suggests that joint stiffness during femoral lengthening may not be determined solely by nail entry direction. Distraction rate, amount of lengthening, soft-tissue tension, patient compliance with rehabilitation, and the duration of external fixation may also influence the joint motions.^5,10,21 Therefore, joint-related complications should be evaluated as multifactorial events rather than consequences of entry direction alone.^10,17,18

The findings of this study should therefore be viewed as exploratory and hypothesis-generating. The results do not support a definitive conclusion that retrograde entry is superior to antegrade entry. Instead, they suggest that retrograde entry may be a viable option in selected femoral LON cases when performed by an experienced surgeon and when careful preoperative planning supports its use. The clinical value of the study lies in showing that retrograde entry, although less commonly preferred because of concerns related to intra-articular knee entry, may produce comparable outcomes in carefully selected patients.

This study has several limitations. First, the choice of antegrade or retrograde entry was based on the surgeon’s judgment rather than random allocation, and this decision may have been influenced by patient anatomy, diagnosis, deformity characteristics, osteotomy location, planned lengthening amount, and anticipated final alignment. In addition to these factors, its retrospective design introduces an inherent risk of selection bias. Second, the sample size was limited, reducing the statistical power to detect differences in complication rates. Therefore, the lack of a statistically significant difference in complications should not be interpreted as evidence of equivalence. Third, all procedures were performed by a single experienced surgeon, which improves technical consistency but limits generalizability. Fourth, the long inclusion period from 1997 to 2018 may have introduced temporal changes in surgical technique, implant selection, perioperative management, and rehabilitation protocols. Finally, the study does not include patient-reported outcomes, serial gait analysis, or detailed functional recovery measures, which would provide a more comprehensive assessment of clinical outcomes.

Despite these limitations, this study provides useful comparative data on antegrade and retrograde femoral LON procedures from a single-surgeon cohort with long-term experience in limb lengthening. The results suggest that retrograde entry was associated with greater achieved lengthening without an observed increase in overall complication rates in this selected cohort. However, these findings should be interpreted as exploratory and should be confirmed by larger, preferably prospective comparative studies with standardized indications, functional outcomes, and sufficient statistical power to evaluate the complication risks.

Conclusion

In this single-surgeon retrospective cohort, retrograde entry in femoral lengthening over nail was associated with greater achieved lengthening and a higher lengthening percentage compared with antegrade entry. No statistically significant increase in overall complication rates or unfavorable outcome scores was observed in the retrograde group. However, these findings should not be interpreted as evidence that retrograde entry independently allows greater lengthening or carries no additional risk. The choice of entry direction was likely influenced by preoperative case selection, planned amount of lengthening, deformity characteristics, osteotomy location, and surgeon-specific decision-making. Therefore, retrograde entry may be considered a viable option in carefully selected femoral LON cases, but larger prospective studies are needed to clarify its indications, complication profile, and comparative effectiveness.

Take home message

• Femoral lengthening over nail remains a clinically relevant technique despite advances in motorized internal lengthening nails, particularly in selected cases where implant limitations, osteotomy planning, or practical considerations influence treatment choice.

• Retrograde entry was associated with greater achieved lengthening in this single-surgeon cohort, but this finding should be interpreted cautiously because entry direction was likely influenced by case selection, planned lengthening, osteotomy level, deformity characteristics, and surgeon-specific decision-making.

• No statistically significant increase in overall complication burden was observed with retrograde entry, but the study was not powered to establish equivalence or definitive safety; therefore, retrograde entry should be considered a viable option only in carefully selected femoral LON cases.

Footnotes

Author note

This study was conducted at the Department of Orthopedics and Traumatology, Istanbul Faculty of Medicine, Istanbul University.

Acknowledgements

We thank our patients for contributing and sharing all the data for this study. We are grateful for the support of Mr. Erol Al and Mrs. Canan Karagöz, keepers of the Ilizarov Archives at the Department of Orthopedics and Traumatology, Istanbul University, for their tremendous work over more than twenty-five years in obtaining the medical records, photos, and radiological data of the lengthening and reconstruction patients.

ORCID iD

Melih Civan

Ethical considerations

This study was approved by the Institutional Review Board of Istanbul University (approval date and number: 2017/09-06) and was conducted in accordance with the principles of the World Medical Association Declaration of Helsinki. Due to the retrospective design of the study and the use of routinely collected data without any additional patient examination or follow-up contact, informed patient consent was not required. IRB approval is presented in the supplementary material.

Author contributions

Author 1#: Methodology, Investigation, Writing-original draft, Formal Analysis.

Author 2#: Investigation, Data curation, Methodology, Writing-original draft.

Author 3#: Project administration, Supervision, Conceptualization, Writing-review & editing.

Author 4#: Resources, Supervision, Writing-review & editing.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

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