The long-term effect of femoral leg lengthening on muscle strength

Abstract

Introduction:

Callus distraction during leg lengthening procedures often leads to a reduction in muscle strength. This study explores whether this decline is temporary or if it persists long-term, with a follow-up period of 10 years.

Materials and methods:

A cohort of nine patients underwent femoral lengthening with a motorized intramedullary device. We measured the maximum isokinetic concentric torque of the knee extensors and flexors preoperatively, at 2 years and at 10 years postsurgery. For this analysis, we included all patients with a full dataset and a minimum follow-up of 10 years (n = 9). We analyzed the differences between preoperative and postoperative maximal isokinetic torques and compared them with a control group of 10 healthy individuals.

Results:

Before surgery, the median maximal isokinetic torque of the extensor group was higher in the unaffected leg compared to the shorter leg. After leg lengthening, the difference in extension torque between the unaffected and the lengthened legs increased at the 2-year follow-up and even more after 10 years. In contrast, no change was observed in the knee flexor group and there was no significant loss of maximal isokinetic torque in the lengthened leg. In the control group, the comparison between the dominant and nondominant leg showed a difference in knee extension torque of 2.9% and in knee flexion torque of 1.7% in favor of the dominant leg.

Conclusion:

Distraction of the muscle appears to have a higher long-term impact on the muscle properties than previously thought.

Keywords

Limb lengthening leg length discrepancy muscle strength intramedullary lengthening device muscle torque

Introduction

Leg lengthening by callus distraction is an orthopedic technique that is well established for the treatment of long bone deformities. It has seen a remarkable progress through the introduction of intramedullary techniques, especially with the adoption of motorized implants.^1,2 Intramedullary leg lengthening procedures with motorized implants have gained wide acceptance due to their improved patient comfort and the documented decrease of the rate of complications associated with other procedures.^1,3

The pursuit of optimal functional outcomes remains the clinical priority. The process of callus distraction impacts not only the bone but also the surrounding soft tissues. A well-documented concern is that leg lengthening by callus distraction may potentially lead to a decrease of muscle strength.^4,5

In a prior investigation we conducted in 2018, we observed that the muscle strength of knee extensors remained compromised even 2 years following surgery.⁵ We therefore raise a critical question: Is the reduction in muscle strength merely a transient effect or does it represent a long-lasting change? Since there is no long-term data in this domain, we introduce a longer follow-up of 10 years to investigate whether muscle strength demonstrates the capacity to recover over time. The primary objective of this study is to assess the long-term effects on muscle strength a decade after patients have undergone retrograde motorized femoral lengthening. By doing so, we strive to provide deeper insights into the extended postoperative recovery process and contribute to a more informed approach to patient care and postoperative rehabilitation.

Ethical clearance for this investigation was obtained from the local ethics committee (Ethikkomission Nordwest- und Zentralschweiz EKNZ, Number of approval: 2018/01857).

Materials and methods

Patient selection

A patient cohort that underwent leg lengthening between 2007 and 2011 was defined, focusing nine patients with a complete dataset who presented with a median leg length discrepancy (LLD) of 3 cm (range: 2.5–4.3 cm). All subjects underwent retrograde femoral limb lengthening using an intramedullary motorized nail (Fitbone Wittenstein). The surgeries were carried out by a senior orthopedic surgeon with two decades of surgical experience.

Measurements were taken before surgery (t1), at 2 years (t2) and 10 years (t3) after surgery. For the long-term follow-up, we included all patients with a complete dataset and a minimum follow up of 10 years (n = 9). The other patients were lost to follow-up. Three patients were female and six patients were male (Table 2). There was one patient with documented knee flexion of only 120° pre- and postoperatively, none of the other patients showed any documented knee stiffness before or after lengthening. Two valgus deformities and one varus deformity were corrected, the rest of the patients did not have significant angular deformities. The mean residual LLD at 10 year follow-up was 3.7mm. The side of the leg that was shorter was equally distributed (five patients with a left shorter leg and four patients with a right shorter leg). The median age at surgery was 17.4 years (range 15.1–19.5 years) (Table 2). The median duration of follow-up was 10.9 years (range: 10–12.2 years).

Table 1.

Difference in isokinetic torque (affected vs. healthy leg) over a 10-year period following leg lengthening surgery, with a comparison to a control group of healthy individuals (dominant versus nondominant leg).

Measurement	Δ knee extensors ICTmax (%)	Δ knee flexors ICTmax (%)
Preoperative (t1)	−12.3	2.8
2 years post-op (t2)	−13.3	1.9
10 years post-op (t3)	−23.4	0.6
Control group	2.9	1.7

Table 2.

Patient demographics (patients with complete follow-up, n = 9).

Age at surgery	Gender	Side (all femur)	Pathology	LLD in mm
17.5	Female	L	Legg calve Perthes disease	45
17.2	Male	R	Posttraumatic	30
18.9	Male	R	Posttraumatic	24
15.6	Female	R	Hypoplasia of lower extremity	35
16.1	Male	L	Hypoplasia of lower extremity	40
15.3	Female	R	Hip dysplasia	30
19.9	Male	L	Posttraumatic	30
16.8	Male	L	Hypoplasia of lower extremity	35
19.5	Male	R	Multiple hereditary exostoses	45

Surgical technique

The surgical approach for each patient was consistent. Under sterile conditions, the motorized nail was inserted. A small transverse incision, approximately 1 cm below the patella, allowed for transligamentous access through the patellar ligament. The entry point at the trochlea was prepared per standard technique.^6,7 Depending on deformity, the pathway in the bone was prepared according to preoperative planning with rigid reaming as per protocol.⁸ Postoperatively, the lengthening process was initiated within 5–7 days, by the application of induction voltage three times per day at a rate of 0.9 mm per day until the desired limb length was achieved. The intramedullary nails were removed after successful lengthening and consolidation after a period of approximately 1–2 years.

Torque measurements

The primary outcome measure was the isokinetic muscle strength, measured by the maximum isokinetic torque (ICTmax) of the knee’s extensor and flexor muscles. Utilizing the Cybex Humac Norm dynamometer (CSMI Medical Solutions), we quantitatively assessed the ICTmax values in both legs.

The unaffected (nonoperated) leg was tested first with each participant performing five consecutive maximal isokinetic concentric extensions and flexions. These exercises were performed with full range of motion (ROM) and were conducted at a constant velocity of 60° per second. The values were normalized to body weight. The side difference was calculated as percentage of the other side. Therefore body weight or height had no influence on the values provided.

We analyzed the differences between the preoperative and postoperative maximum isokinetic torques (ICTmax) and compared the longer leg to the shorter leg. Maximum isokinetic, concentric torque (ICTmax) of the extensors and the flexors of the knee were measured with a dynamometer (Cybex Humac Norm, CSMI Medical Solutions). The latest measurements were done with the Biodex System, 4 Pro (Biodex Medical Systems, Shirley NY, USA).

We analyzed the differences between preoperative and postoperative torque measurements of the lengthened leg compared to the unaltered leg.

These measured values were compared to a control group (dominant versus non-dominant leg) of 10 healthy individuals (age and body mass index matched) without LLD. For statistical analysis we used SPSS (IBM SPSS Statistics, Version 27, IBM Corporation, 2020, USA) and an independent sample as well as a paired samples t-test and the Levene-test.

Results

The preoperative assessment revealed that the median maximum isokinetic torque of the knee extensors was 12.3% greater in the unaffected, nonoperated leg compared to the shorter leg scheduled for lengthening. A follow-up at 2 years postsurgery indicated that this difference had slightly increased, with the normal leg demonstrating a 13.3 % higher torque than the lengthened leg. At the 10-year mark this increased to 23.4 % (Table1, Table 3, Figures 1 and 2).

Table 3.

Mean side-to-side differences (One standard deviation) in maximum isokinetic torque (affected versus healthy leg) over a 10-year period following leg lengthening surgery, with a comparison to a control group of healthy individuals (dominant versus nondominant leg).

Muscle group	Patients preoperatively	Patients at 2-year follow-up	Patients at 10-year follow-up	Control group
Extensors (%)	−12.3 (17.9)	−13.3 (23.0)	−23.4 (17.2)	2.9 (8.2)
Flexors (%)	2.8 (18.4)	1.2 (20.4)	0.6 (6.1)	1.7 (8.9)

Negative values indicate that the affected (or nondominant, respectively) had lower torques than the healthy (or dominant, respectively) leg.

Figure 1.

Development of maximal isokinetic torque differences in knee extensors and flexors post-leg lengthening.

Figure 2.

Example of postoperative measurement of maximum isokinetic torques.

In contrast, the knee flexor muscles did not follow the same pattern. The initial measurements showed no discrepancy in strength between the normal and shorter legs. This muscle group maintained its strength over time in the lengthened leg, without a reduction in muscle force. The comparison of measurements of the torque difference in one patient over time were not statistically significant (Table 4).

Table 4.

Comparison between side-to-side differences in maximum isokinetic torques between time points in patients.

Muscle group	2-Year follow-up – preoperatively		10-Year follow-up – preoperatively		10-Year follow-up – 2-year follow-up
Muscle group	Mean difference [95% CI]	p value	Mean difference [95% CI]	p value	Mean difference [95% CI]	p value
Extensors (%)	−1.0 [−20.2, 18.2]	0.911	−11.1 [−26.3, 4.2]	0.133	−10.1 [−28.2, 8.0]	0.235
Flexors (%)	−1.6 [−10.8, 7.6]	0.696	−2.2 [−14.9, 10.4]	0.694	−0.6 [−15.0, 13.7]	0.922

The control group (n = 10) exhibited much narrower differences in muscle strength, with the dominant leg showing a 2.9% higher torque in knee extensors and 1.7% in knee flexors relative to the nondominant leg. The differences between the extensor torques of the cohort and the extensor torques of the control group were significant preoperatively (p = 0.039) and after 10 years (p = 0.001; Table 5). The differences between the flexor torques of the cohort and the control group were not significant.

Table 5.

Comparison between side-to-side differences in maximum isokinetic torques between patients and controls for each time point.

Muscle group	Preoperatively – controls		2-Year follow-up – controls		10-Year follow-up – controls
Muscle group	Mean diff [95% CI]	p value	Mean diff [95% CI]	p value	Mean diff [95% CI]	p value
Extensors (%)	−15.3 [−29.6, −0.9]	0.039	−16.2 [−34.3, 1.8]	0.073	−26.3 [−39.2, −13.5]	<0.001
Flexors (%)	4.5 [−9.2, 18.3]	0.496	2.9 [−12.1, 17.9]	0.686	2.3 [−5.2, 9.8]	0.529

Discussion

The long-term effects of callus distraction on muscle strength and function are areas of ongoing research. While some studies indicate that muscle strength may eventually recover to a certain extent, others have shown that deficits may persist, leading to functional limitations. Research by Bhave et al.⁴ suggested that patients could regain preoperative levels of muscle strength with intensive physical therapy, while other studies such as those by Krieg et al.¹ point to persistent weakness even years after the procedure.

Clinical and experimental studies describe that muscle adaptation during distraction osteogenesis is complex and can lead to a decrease in muscle strength. A study by Simpson et al.⁹ found that during limb lengthening procedures, the muscles undergo significant changes, including alterations in sarcomere number and length, which can contribute to the reduction in muscle strength observed clinically. Additionally, a study by Liantis et al.¹⁰ highlighted that the rate of distraction can influence the degree of muscle adaptation and the potential for recovery of muscle function.

Bhave et al.⁴ explored the changes of muscle strength following femoral lengthening. Their research compared the conventional Ilizarov apparatus with the method of lengthening over a nail, focusing on hamstring and quadriceps strength and joint mobility before and after the procedures. They concluded that quadriceps strength was largely unaffected. In 34 of 48 femoral lengthenings, quadriceps muscle strength increased or returned to preoperative level.

Changes in muscle strength postlengthening are multifactorial. None of our patients had documented changes in their knee mobility pre- and postlengthening. We do not have detailed information about the rehabilitation protocol, which limits our findings. One might argue that immediate postsurgery rehabilitation protocol has no more influence on the results after 10 years. None of our patients suffered from neurological changes.

In a recently published 10-year follow-up study after intramedullary femoral lengthening,¹¹ the long-term clinical outcomes and radiological conditions of the knee after leg lengthening were evaluated. The MRI assessments conducted as part of this investigation revealed that although all patients reported being pain-free with a preserved ROM 10 years after surgery, a notable proportion exhibited fibrosis of Hoffa’s fat pad as well as moderate-to-severe cartilage defects within the trochlear groove. Clinically, joint function was found to be comparable between the operated and nonoperated legs showing no noticeable deficits in movement or functionality.

The MRI component of that study identified atrophy of the medial vastus muscle in a majority of the operated knees (10 out of 13), a condition not observed in the contralateral nonoperated knees.¹¹ The atrophy of the quadriceps muscle in the operated legs could potentially explain the differences in muscle strength observed. On the one hand, the atrophy could be an inherent preexisting condition due to congenital deformity with altered biomechanics. On the other hand, as a previous biomechanical analysis suggest, it could be a direct consequence of the intramedullary lengthening procedure, which may inherently impede muscle strength. The muscle weakening could potentially be a reactive adaptation to the distraction process, characterized by increased muscle stiffness and a decreased ability of the muscle to stretch and contract rapidly in response to the lengthening process. Barker et al.¹² reported a 2 year outcome after femoral lengthening with external fixators in 16 patients, which showed a significant difference of muscle strength in the operated versus the affected leg at all timepoints. They showed slightly reduced muscle strength, more in the quadriceps than the hamstrings, which is consistent with our result. Of note, they looked at patients that were lengthened with external fixation, not intramedullary nailing, which might be a limitation in comparing this study to ours. However, the effect on the muscles after lengthening should be similar. Long-term outcome of 10 years was not provided by these authors. Holm et al.¹³ reported no long-term reduction in muscle strength in a cohort of nine patients that underwent bilateral femoral lengthening with external fixators. They did not have the unaffected side to compare to. They also reported initially reduced quadriceps torque, which is consistent with our findings. There are further studies needed to investigate whether intramedullary lengthening outcomes regarding muscle strength differ to lengthening with external fixators. However, in current protocols, adult patients rarely undergo femoral lengthenings with external fixators anymore.

Another limitation is that we did not measure isometric strength, but only isokinetic strength. It was not measured in the initial measurements and therefore we would have had no long time comparison.

Our findings suggest a long-term and specific impact of femoral lengthening on extensor muscle strength, while flexor strength remains comparatively stable both in the short and long term. The exact mechanisms and contributory factors behind these enduring changes remain unclear. They could potentially originate from alterations at various anatomical levels—ranging from the entire muscle (alterations in length and inherent atrophy) to the microscopic level of muscle fascicles (variations in length and orientation, microvascular circulation and neural innervation) and down to the muscle fibers themselves (fiber damage and excessive connective tissue proliferation). Future investigations, incorporating muscle biopsy studies, might add new knowledge to these remaining questions and are subject of ongoing research.

The practical significance of these differences in muscle strength in everyday activities remains unclear. In daily life, the need for maximal force exertion is infrequent; Therefore, the patients might not perceive any substantial functional limitation. This aspect highlights the complexity of quantifying the real-world impact of muscle strength variations after surgery has been performed.

Our study is limited due to its retrospective and single-center nature and the small sample size. The small sample size might impact our studies statistical power, and there is a risk for a type II error. Therefore, multicenter, prospective studies are needed in the future to be able to generalize the results and gain more insight in muscle strength after leg lengthening.

Conclusion

Prior investigations had already highlighted the phenomenon of muscle strength diminishment following leg lengthening procedures.¹ The extent to which the muscle distraction impacted strength was unexpectedly more profound than we initially expected. Our current research reveals that the knee extensors strength does not fully recover even over an extended period of 10 years after femoral leg lengthening. The average lengthening in our cohort was 3 cm, which represents a modest amount of lengthening. The findings regarding muscle strength for more substantial leg lengthening might differ. This would be interesting to explore with future studies.

From a clinical perspective, despite the discrepancies in muscle strength and the radiological manifestations observed a decade after the leg lengthening procedure, patients reported no subjective complaints or functional limitations in the operated knees. This difference between objective findings and patient experience raises questions about the impact of these physiological changes on daily and overall quality of life, indicating that patients may not perceive the reduction in strength or radiological alterations as detrimental. Prospective studies measuring patient related outcomes would be useful to determine the significance of our results.

Supplemental Material

sj-docx-2-cho-10.1177_18632521261417907 – Supplemental material for The long-term effect of femoral leg lengthening on muscle strength – A 10-year follow-up

Supplemental material, sj-docx-2-cho-10.1177_18632521261417907 for The long-term effect of femoral leg lengthening on muscle strength – A 10-year follow-up by Bernhard Maria Speth, Kira A. Barlow, Marc Schmid, Corina Nüesch, Petros Ismailidis and Andreas Heinrich Krieg in Journal of Children's Orthopaedics

Supplemental Material

sj-pdf-1-cho-10.1177_18632521261417907 – Supplemental material for The long-term effect of femoral leg lengthening on muscle strength – A 10-year follow-up

Supplemental material, sj-pdf-1-cho-10.1177_18632521261417907 for The long-term effect of femoral leg lengthening on muscle strength – A 10-year follow-up by Bernhard Maria Speth, Kira A. Barlow, Marc Schmid, Corina Nüesch, Petros Ismailidis and Andreas Heinrich Krieg in Journal of Children's Orthopaedics

Footnotes

Authors contributions

Dr. Speth, Bernhard Maria: Measurements and conception of manuscript

Dr. Barlow, Kira Anika: Statistics and writing of manuscript

Dr. Schmid, Marc: Measurements

Nüesch, Corina: Measurements and help with statistics

PD Dr. Ismailidis, Petros: Correction and writing

Prof. Dr. Krieg, Andreas Heinrich: Conception of study, writing assistance

Data availability statement

The datasets generated and analyzed during the current study are not publicly available due to the data protection of the singular patient and a small patient number. The datasets are available from the corresponding author on reasonable request at any time.

Declaration of conflicting interests

The authors declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: The authors wish to disclose that there are no conflicts of interest that could potentially influence the interpretations of the data within this article. One of our contributors, AK, has previously received consultancy fees from ORTHOFIX S.R.L. However, this has not biased the research findings or the presented viewpoints. The remaining contributors have no financial or personal relationships that could be seen as a conflict of interest regarding this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research was supported in part by the Kämpf Bötschi Foundation, Basel, Switzerland. The sponsors neither had an influence on study design, the collection, analysis, and interpretation of data, the preparation of the article, nor on the decision to submit the article for publication. The views expressed in this article are exclusively those of the authors.

Ethical statement

This study has been approved by the local ethics committee (Ethikkomission Nordwest- und Zentralschweiz EKNZ, Number of approval: 2018/01857).

Informed consent

All patients gave written consent to take part in the study. No consent was withdrawn.

ORCID iDs

Corina Nüesch

Andreas Heinrich Krieg

Supplemental material

Supplemental material for this article is available online.

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