Predictable regeneration and protective effect against ankle valgus following non-vascularized fibular graft harvest in children

Abstract

BACKGROUND

Non-vascularized fibular grafts are frequently used in pediatric orthopaedics because of their structural strength and low donor-site morbidity. Preservation of the periosteal sleeve may permit regeneration of the harvested fibula; however, the predictability of regeneration and its influence on ankle alignment remain incompletely understood. This prospective study evaluated the timing of fibular regeneration following long-segment fibular graft harvest in children and its association with ankle valgus deformity.

AIM

To analyse the timing of fibular regeneration after long segment fibular graft harvest in children and its association with ankle valgus deformity.

METHODS

Sixteen children (27 operated limbs) aged ≤ 12 years undergoing long-segment non-vascularized fibular graft harvest were prospectively followed. Radiographic assessment of the donor site was performed at 6 weeks, 3 months, 6 months, and final follow-up. Fibular regeneration was defined as radiological continuity across the harvested segment. Ankle valgus was assessed using the lateral distal tibial angle and distal fibular station (Malhotra grading). Associations between regeneration and ankle valgus were analyzed using the Pearson χ² test.

RESULTS

Mean follow-up was 25.8 ± 17.9 months. Complete fibular regeneration was observed in 33.3% of limbs at 3 months, 63.0% at 6 months, and 77.8% at final follow-up. Mean time to regeneration was 5.0 ± 2.9 months. The mean lateral distal tibial angle decreased significantly from 89.1° preoperatively to 87.8° at 6 months (P = 0.047) and 86.6° at final follow-up (P = 0.001). At final follow-up, ankle valgus was present in 83.3% of limbs without regeneration compared with 33.3% of regenerated limbs. Fibular regeneration was associated with significantly lower odds of ankle valgus (odds ratio = 0.10, P = 0.030).

CONCLUSION

Fibular regeneration following non-vascularized graft harvest in children is common when the periosteal sleeve is preserved, with most cases achieving continuity within 6 months. Successful regeneration appears to be associated with a low incidence of ankle valgus deformity, underscoring the importance of meticulous periosteal preservation and postoperative surveillance.

Key Words: Fibular regeneration; Non-vascularized fibular graft; Ankle valgus deformity; Periosteal preservation; Donor-site morbidity

Core Tip: Fibular regeneration following non-vascularized fibular graft harvest in children is common when the periosteal sleeve is preserved, with most cases achieving continuity within six months. This prospective study demonstrates that successful regeneration is associated with a substantially lower incidence of ankle valgus deformity, highlighting its protective role in maintaining lateral ankle stability. However, regeneration is not universal, and valgus deformity may occur despite regeneration, emphasizing the need for meticulous surgical technique, preservation of the periosteum, and serial postoperative surveillance of the donor site.

INTRODUCTION

Non-vascularized fibular grafts are widely used in paediatric orthopaedics for indications such as obtaining unions, osseous reconstructions and managing bony defects[1-5]. The fibula provides an optimal graft owing to its cortical strength, ease of harvest, and relatively low donor-site morbidity. A distinct advantage in children is the potential for regeneration of the fibula at the donor site, particularly when the periosteal sleeve is preserved[6,7].

Although previous studies have suggested that fibular regeneration occurs reliably within a few months, the timing and completeness of this process remain variable and not entirely predictable. Failure of regeneration may compromise the lateral column of the leg and predispose to progressive ankle valgus deformity, which can adversely affect lower limb biomechanics and long-term function[8-12].

Despite its clinical relevance, there is limited prospective evidence evaluating the temporal pattern of fibular regeneration and its relationship to ankle alignment. Although previous studies have reported donor-site regeneration following non-vascularized fibular harvest, nearly all have been retrospective with heterogeneous follow-up intervals and limited longitudinal evaluation of ankle alignment. Consequently, the precise timeline of fibular regeneration and its temporal relationship with development of ankle valgus remain incompletely understood. The present prospective study was therefore designed to serially evaluate fibular regeneration using standardized radiographic follow-up and to investigate its association with ankle valgus after long-segment fibular graft harvest in children. We hypothesized that fibular regeneration following periosteum-preserving non-vascularized graft harvest follows a predictable temporal pattern and that successful regeneration is associated with a lower incidence of ankle valgus.

MATERIAL AND METHODS

This prospective observational study was conducted after obtaining approval from the Institutional Ethics Committee. Children aged 12 years or younger who required long-segment non-vascularized fibular grafts for procedures including spinal fusion, osteosynthesis, or filling of bone defects following cyst curettage were included. Both unilateral and bilateral fibular harvests were considered, each counted as a distinct unit. In all cases, a standardized surgical technique was used as described in earlier studies[6,13]. All fibular grafts were harvested from the diaphyseal region using a standardized subperiosteal technique. Adequate proximal and distal fibular remnants were preserved in all patients, and meticulous care was taken to maintain the integrity of the periosteal sleeve to facilitate regeneration. The length of fibula harvested was individualized according to patient age and the reconstructive requirements of the primary procedure.

Radiographic evaluation of the donor site was performed using a weight-bearing scanogram preoperatively and postoperatively at 6 weeks, 3 months, 6 months, and at final follow-up. The primary outcome measure was the timing of longitudinal fibular regeneration, defined as radiological continuity across the harvested segment. Secondary outcomes included the development of ankle valgus deformity, assessed initially at 6 months and again at final follow-up, using the lateral distal tibial angle (LDTA) and distal fibular station as per Malhotra grading (Figures 1 and 2)[14]. For this study, ankle valgus was defined as an LDTA of less than 84 degrees, a fibular station greater than grade 1, or both.

Figure 1 Measurement of lateral distal tibial angle. LDTA: Lateral distal tibial angle.

Figure 2 Malhotra grading for paediatric ankle valgus. A: Grade 0: Fibular physis at or below the level of the tibial plafond; B: Grade 1: Fibular physis between plafond and distal physis of tibia; C: Grade 2: Fibular physis at the level of distal tibial physis; D: Grade 3: Fibular physis above the distal tibial physis. The degree of ankle valgus is determined based on the level of the fibular physis.

Statistical analysis

Statistical analysis was performed to evaluate changes in LDTA over time and to determine the association between fibular regeneration and ankle valgus, with significance set at P < 0.05.

RESULTS

A total of 16 children, comprising 27 operated limbs, were included in the study. The cohort included 10 males and 6 females, with a mean age of 6.1 years (SD = 2.8 years; range 3.5-11.5 years). The mean duration of follow-up was 25.8 months (SD = 17.9 months; range 6-72 months). The indications for fibular graft harvest included spinal fusion in 8 patients, long bone osteosynthesis in 5 patients, and management of cystic bone lesions in 3 children. Bilateral fibular graft harvest was performed in 11 children, while unilateral harvest was obtained in 5 children.

Radiological evaluation demonstrated that no limb exhibited continuous fibular regeneration at 6 weeks postoperatively. At 3 months, complete longitudinal continuity was observed in 9 of 27 limbs (33.3%), which increased to 17 limbs (63%) at 6 months. At final follow-up, 21 limbs (77.8%) demonstrated complete regeneration (Figure 3). The mean time to fibular regeneration was 5 months (SD = 2.9 months; range 3-12 months). Persistent non-continuity was noted in 10 limbs (37%) at 6 months and in 6 limbs (22.2%) at final follow-up, all of which were localized to the distal third of the fibula.

Figure 3 Serial radiograph of lower limb where bilateral fibula was harvested for spinal fusion surgery. A: Preoperative; B: Immediate postoperative; C: 3 months post-surgery; D: 6 months post-surgery; E: Antero-posterior and Lateral radiograph of bilateral leg taken at final follow-up showing complete union. AP: Antero-posterior; Preop: Preoperative; Post-op: Post-operative.

Analysis of ankle alignment revealed a progressive decrease in LDTA over time. The mean preoperative LDTA was 89.1 degrees (SD = 3.1 degrees), which decreased to 87.8 degrees (SD = 2.8 degrees) at 6 months and further to 86.6 degrees (SD = 2.8 degrees) at final follow-up. These changes were statistically significant when compared to preoperative values (P = 0.047 at 6 months and P = 0.001 at final follow-up). Malhotra grade 2 or higher was observed in 6 limbs at 6 months and in 4 limbs at final follow-up (Table 1).

Table 1 Summary of findings of the study, n (%).

Total number of cases	16
Total number of fibulae harvested	27
Mean age	6.1 years (SD = 2.8 years; range 35-11.5 years)
Mean follow-up	25.8 months (SD = 17.9 months; range 6-72 months)
Male:Female	10:6
Unilateral:Bilateral	5:11
Mean LDTA
Preoperative	89.1 degrees (SD = 3.1 degrees)
6 months	87.8 degrees (SD = 2.8 degrees)
Final follow-up	86.6 degrees (SD = 2.8 degrees)
Malhotra grade
Preoperative	Grade 0: 9; grade 1: 18; grade 2: 0; grade 3: 0
6 months	Grade 0: 2; grade 1: 19; grade 2: 6; grade 3: 0
Final follow-up	Grade 0: 5; grade 1: 18; grade 2: 3; grade 3: 1
Complete regeneration
3 months	9 (33.3)
6 months	17 (63)
Final follow-up	21 (77.8)
Incomplete regeneration	6 (22.2)

LDTA: Lateral distal tibial angle.

At 6 months, ankle valgus was present in 7 of 10 limbs (70%) where regeneration failed, while 5 of 17 limbs (29.4%) had ankle valgus despite regeneration, and 3 of 10 limbs (30%) did not develop ankle valgus despite failed regeneration. At final follow-up, ankle valgus deformity was present in 5 of 6 limbs (83.3%) in which fibular regeneration had failed, whereas 7 of 21 limbs (33.3%) with successful regeneration also demonstrated valgus alignment. Notably, 1 of 6 limbs (16.6%) without regeneration did not develop valgus deformity. Statistical analysis using the Pearson χ² test demonstrated that fibular regeneration was significantly associated with lower odds of ankle valgus (odds ratio = 0.10; 95%CI: 0.01-1.03 P = 0.03) (Table 2).

Table 2 Association between fibular regeneration and development of ankle valgus following non-vascularized fibular graft harvest in children at 6 months and final follow-up.

Fibula regeneration	Ankle valgus present	Ankle valgus absent	Odd ratio (95%CI)	P value1
At 6 months
Present	5	12	0.18 (0.03-0.99)	0.040
Absent	7	3
At final follow-up
Present	7	14	0.10 (0.01-1.03)	0.030
Absent	5	1

¹Pearson χ² test.

The four cases that failed to achieve union at 6 months but subsequently united by the final follow-up showed no apparent association between regeneration and ankle valgus. Two of these cases never developed ankle valgus, while the remaining two had persistent ankle valgus despite successful regeneration at final follow-up.

DISCUSSION

The present prospective study demonstrates that fibular regeneration following non-vascularized fibular graft harvesting in children is a reliable biological phenomenon when the periosteal sleeve is preserved. The study included patients undergoing fibular harvest for spinal fusion, osteosynthesis and treatment of bone cysts. Although these indications differ clinically, the donor-site harvest technique and postoperative protocol remained identical for all patients, reducing potential variability in donor-site regeneration. Progressive longitudinal regeneration was observed over time, with 63% of limbs demonstrating complete continuity at 6 months and 77.8% at final follow-up (Figure 4). The mean regeneration time of 5 months observed in this series is comparable to earlier reports describing the remarkable osteogenic potential of the preserved fibular periosteum in paediatric patients[6]. Steinlechner and Mkandawire[3] reported successful fibular regrowth in the majority of children following non-vascularized fibular transfer, emphasizing that periosteal preservation forms the biological basis of regeneration. Similarly, Agarwal and Kumar[13] demonstrated regeneration rates ranging from 55% to 71% at 6 months in a retrospective pediatric series, findings that are largely consistent with the current prospective observations.

Figure 4 Plain radiograph of a patient where fibula failed to unite initially but achieved complete regeneration at one year follow up. A: Preoperative; B and C: Radiograph taken at 6 months showing incomplete regeneration; D and E: One year post surgery radiograph showing complete regeneration. Preop: Preoperative; Post-op: Post-operative.

Despite the encouraging regenerative potential, fibular regeneration was not a universal phenomenon. Persistent fibular non-continuity was observed in 22.2% of limbs at final follow-up, and notably, all non-regenerates involved the distal third of the fibula (Figure 5). This observation corroborates previous literature suggesting that the distal fibula may represent a relative biological “watershed zone”. Anatomical studies have shown that nutrient foramina are predominantly concentrated in the proximal fibula, while the middle and distal thirds possess relatively limited vascularity[15]. Goh et al[16] proposed that disruption of vascular supply following graft harvest may therefore disproportionately affect distal regeneration. In addition, the distal periosteum is often thinner and more adherent, making atraumatic preservation technically challenging in this region during harvest. These anatomical and biomechanical considerations may explain the consistent localization of non-regeneration to the distal third in the present series.

Figure 5 One and a half years follow-up of a case where long segment graft harvest from bilateral fibula shows failure to achieve complete regeneration at final follow-up. A: Preoperative; B: Immediate post-operative; C: 6 months follow-up; D: Final follow-up. Serial plain radiograph taken at preoperative, immediate post op, 6 months follow-up, final follow-up. Preop: Preoperative; Post-op: Post-operative.

An important finding of this study was the progressive deterioration in ankle alignment following fibular harvest. The mean LDTA decreased significantly over time, indicating gradual valgus inclination of the ankle. This supports previous observations by González-Herranz et al[11], who reported ankle valgus deformity after fibular resection in children and emphasized the mechanical role of the fibula in maintaining ankle stability. Most of the muscles acting on the foot and ankle originate from the posterior and lateral aspects of the tibia and fibula, whereas the medial subcutaneous surface of the tibia is largely devoid of muscular attachments. This asymmetric distribution of soft-tissue forces creates a persistent lateral bending moment on the tibia during growth and weight-bearing. Under normal circumstances, the fibula functions as a critical lateral stabilizing strut, counterbalancing these deforming forces and maintaining coronal plane alignment of the leg. Analogous to the string of a bow, the fibula provides lateral support to the tibia and ankle mortise, resisting lateral thrust and preventing progressive valgus angulation of the distal tibia. The fibula contributes approximately one-sixth of axial load transmission across the leg and serves as an important lateral stabilizer of the ankle mortise. In addition to providing structural support, it maintains congruity of the distal tibiofibular articulation and contributes to preservation of normal coronal alignment during skeletal growth. Disruption of fibular continuity therefore has the potential to alter lower-limb biomechanics and predispose to progressive ankle valgus.

A mild degree of physiological ankle valgus is a normal adaptation that facilitates stable bipedal stance and efficient load transmission through the plantigrade foot. The fibula, being longer than the tibia distally, plays an important role in maintaining congruency of the ankle mortise and preventing lateral talar tilt. By acting as a lateral buttress, it helps preserve the LDTA and ensures even distribution of forces across the ankle joint.

Harvesting of the fibula disrupts this biomechanical equilibrium. Loss of fibular continuity renders the distal fibular segment relatively mobile and diminishes its ability to provide lateral restraint to the ankle mortise. Consequently, the talus tends to tilt laterally, leading to progressive reduction in LDTA and worsening ankle valgus. Furthermore, loss of fibular integrity alters normal load-sharing mechanics, resulting in increased stresses across the distal tibial physis. Over time, proximal migration of the distal fibular remnant, combined with asymmetric loading of the distal tibial growth plate, may produce progressive lateral physeal wedging and valgus malalignment of the ankle[17-20].

The present study further demonstrates a strong association between successful fibular regeneration and reduced incidence of ankle valgus. Limbs with regeneration had significantly lower odds of valgus deformity. These findings reinforce the concept that restoration of fibular continuity re-establishes lateral column stability and is associated with lower risk of progressive deformity. Similar conclusions were drawn in earlier retrospective studies by Agarwal et al[20], where ankle valgus was considerably more frequent in non-regenerated donor fibulae.

However, the relationship between regeneration and valgus deformity was not absolute. One limbs without regeneration did not develop valgus, whereas several regenerated limbs still demonstrated valgus alignment. This indicates that ankle valgus following fibular harvest is likely multifactorial rather than solely dependent on regeneration status. Factors such as distal fibular remnant length, integrity of the syndesmotic and ligamentous structures, physeal responsiveness, duration of altered biomechanics, and individual variations in growth may all influence deformity development. Furthermore, even regenerated fibulae may not completely restore normal biomechanics if regeneration is delayed, malaligned, or structurally inadequate. We found an altered LDTA in regenerated harvested fibulae at 6 months and final follow-up compared to preoperative values.

The clinical implications of these findings are considerable. Preservation of the periosteal sleeve should be regarded as a critical technical step during fibular graft harvesting in children. Extra careful subperiosteal dissection and protection of the distal fibular remnant may maximize regenerative potential and minimize donor-site morbidity. Additionally, serial postoperative radiographic surveillance of the harvest site is essential, particularly during the first 6-12 months, when regeneration and valgus changes evolve most rapidly. Early recognition of progressive ankle valgus may permit timely intervention with growth modulation procedures such as medial distal tibial hemiepiphysiodesis and Lagenskold procedure[21,22].

The present study has several limitations. The sample size was relatively small, reflecting the uncommon and heterogeneous indications requiring pediatric fibular graft harvest. Graft lengths (according to child’s age) varied, potentially influencing regeneration dynamics and mechanical outcomes. Functional outcomes and gait analysis were not evaluated, limiting assessment of the true clinical impact of radiological abnormalities. Eleven children underwent bilateral fibular harvest. Accordingly, some observations were not statistically independent, and the results should be interpreted with this limitation in mind. Nevertheless, the prospective design, sequential radiographic assessment, and longitudinal evaluation of regeneration and ankle alignment provide important evidence regarding donor-site behaviour following paediatric fibular graft harvesting. An identical surgical technique and diaphyseal fibular harvest remained uniform for all studied harvests.

Overall, this study highlights that fibular regeneration is common but not guaranteed following non-vascularized graft harvest in children, and successful regeneration appears to be associated with a lower incidence of ankle valgus. Careful surgical technique and vigilant harvest site monitoring post-procedure remain essential to optimize donor-site outcomes in the paediatric population.

CONCLUSION

Non-vascularized fibular graft harvest in children, when performed with preservation of the periosteal sleeve, results in a high rate of longitudinal regeneration, with most cases achieving continuity within the first 6 months and nearly 80% by final follow-up. Fibular regeneration is associated with a significantly reduced risk of ankle valgus deformity, highlighting its protective role in maintaining lateral column stability. However, given that regeneration is not universal and valgus deformity may still occur, careful postoperative surveillance remains essential to ensure early identification and appropriate management of evolving deformities.