Adductor magnus muscle transfer to restore knee extension: Anatomical studies and clinical applications

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Summary

Background

Loss of knee extension causes significant impairment. Though nerve-based reconstruction is preferable in cases of femoral nerve palsy or injury, these surgeries are not always appropriate if the pathology involves the quadriceps muscles or presentation too late for muscle reinnervation. Muscle transfers are another option that has been underutilized in the lower extremity. We describe the successful restoration of knee extension by adductor magnus muscle transfer without functional donor morbidity, along with anatomical considerations.

Methods

Ten fresh frozen cadaveric lower limbs were dissected at the groin and thigh. In addition, three patients presented with femoral nerve palsy for which nerve-based reconstruction was not appropriate because of late presentation. In these patients, adductor magnus muscle transfers were performed, along with sartorius, gracilis, and tensor fasciae latae transfers if available and healthy.

Results

In cadavers, the pedicle for the adductor magnus is at the level of the gracilis and adequate for muscle transfer, with sufficient weavable tendon length. The only major structure at risk is the femoral neurovascular bundle, which is in a reliable anatomic position. Two patients recovered 4/5 active knee extension and ambulation without assistive devices. A third required reoperation for a loosened tendon weave, after which the noted improved stability and strength with ambulation but did not regain strong active knee extension and continued to require a cane.

Conclusions

We present a novel reconstructive approach for loss of quadriceps function in patients, which yields good clinical outcomes, with anatomic and technical details to demonstrate the utility of this technique. Ongoing evaluation of optimal technique and rehabilitation to maximize functional outcomes is still needed.

Introduction

Loss of knee extension is a devastating condition that produces significant disability, including the inability to run, climb stairs, drive, and even ambulate without supportive aids. Most cases are iatrogenic in nature, but traumatic and malignant causes are possible.1, 2, 3

Reconstructive options after loss of quadriceps function are poorly described despite its disabling impact.4,5 Nerve grafting is widely used, but the proximal stump can be difficult to identify and access.6 Our group7 and others8, 9, 10 have pioneered nerve transfers from the obturator to the femoral nerve in order to restore function. However, many patients present after terminal atrophy of the target muscle sets in or with injury or pathology involving the quadriceps muscles, precluding nerve transfers. More aggressive options including free functional flaps have been described, but are not tolerated by all.11, 12, 13, 14

In patients who are not appropriate candidates for nerve-based or microvascular reconstruction, pedicled muscle transfers remain an option. These have been performed for decades in the upper extremity with excellent results,15, 16, 17 though they have not been as well-described in the lower extremity. Optimally, the donors are expendable and synergistic with the recipient, as the donor performs one function along a straight line of pull.18 The donor also needs strength and excursion to match the desired motion, which limits lower extremity reconstruction due to the large biomechanical demand on donors as compared to the upper extremity.

Previous attempts at using muscle transfers in the lower extremity have focused on the plantarflexion at the Achilles tendon19, 20, 21, 22, 23 and providing support to an intact quadriceps with knee flexors, not restoring knee extension.24,25 Previous attempts at restoring knee extension used knee flexors and required extensive transposition and training antagonistic muscles with a spiral line of pull, leading to suboptimal results.26

We propose adductor magnus as a potentially more appropriate donor for knee extension. Given its location and function, it is synergistic with the quadriceps and requires less dissection and transposition while providing a straighter line of pull than a hamstring donor. Further, it remains functional in an isolated femoral nerve palsy as its innervation is from the obturator nerve. Its relatively larger size compared with other described options, such as gracilis or sartorius,*** and expendable function suggests that it may better handle the large load required to replacing quadriceps function without downgrading hip adduction, making it a more ideal donor either alone or in combination with other muscles.

We describe the adductor magnus as a muscle transfer to restore knee extension in patients with femoral nerve palsy that are too late for nerve-based reconstruction, in addition to other muscle donors, such as the gracilis, sartorius, or tensor fascia latae (TFL), to maximize stabilization and strength. We detail the anatomic considerations of this transfer and report the results of three patients who have undergone this procedure.

Section snippets

Anatomic study of the adductor magnus

Anatomy of the adductor magnus, including external landmarks, orientation and structure of the vascular pedicle, the length of available tendon for weave, the proximal musculotendinous junction, location of the adductor hiatus, and relationship of the tendinous insertion to external landmarks was dissected in nine limbs.

The adductor magnus is not palpable on the medial aspect of the thigh, but its tendon travels posterior to the palpable adductor longus across all studied limbs. The distal

Surgical technique

With the patient supine, the posterior border of the adductor longus was marked from the palpable femoral pulse to the medial aspect of the knee, with the most distal incision curved anteriorly to allow exposure of the patellar tendon (Figure 4). The gracilis and sartorius are easily identified and retracted laterally and medially, respectively, and next the adductor magnus identified between, crossing underneath the sartorius distally (Figure 5).

The adductor magnus insertion is then located at

Post-operative rehabilitation protocol

Patients were discharged as non-weightbearing with a knee immobilizer fixing the joint in extension for a minimum of 6 weeks. Ambulation during this time was accomplished with a walker or crutches. Patients were transitioned to full weightbearing around 6–8 weeks after surgery while still braced in extension.

At 8 weeks post-operatively, physical therapy was started with a focus on motor re-education and antigravity exercises for all actions in the thigh, including hip motion, knee extension,

Patient 1

A 52-year-old woman presented with failure to extend her right knee 1 year after a right total hip replacement, and frequent falls due to her instability and weakness. She had no return of function, with Medical Research Council (MRC) 0/5 strength, numbness in the femoral nerve distribution, consistent with an isolated femoral nerve palsy and intact obturator nerve function.

Given the time since injury, she was not a candidate for nerve transfers as terminal atrophy of the quadricep muscles had

Discussion

In nerve injuries, nerve-based reconstruction is not feasible, if terminal atrophy of the target muscle and its neuromuscular junction has occurred.30 There may be involvement of the quadriceps muscles due to injury or resection of malignancy. In these scenarios, muscle transfers remain the only means to restore function, taking expendable, functional donors, and transferring their tendons to perform lost function. In line with the tenants of tendon transfer in the upper extremity, these are

Conclusions

Loss of knee extension profoundly affects the quality of life of patients. We propose the adductor magnus muscle transfer as a new reconstructive option to reconstruct quadriceps function in patients with femoral nerve palsy outside the window for nerve-based reconstruction. Further, the adductor magnus muscle transfer remains a possibility to augment function in those who have undergone nerve-based reconstruction with suboptimal results or requiring more power. Our findings are supported by

Declaration of Competing Interest

None.

Ethical Approval

N/A

Funding

None.

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    Presented at: Plastic Surgery the Meeting (ASPS) 2019 in San Diego, California on September 22, 2019. Awarded Best Reconstructive Paper in Session.

    This study conforms to the Declaration of Helsinki. This study was performed according to the STROBE guidelines for patient series.

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