An atypical case of calf pain: Plantaris tendon axial instability

Abstract

Plantaris tendon (PT) might induce calf or Achilles pain. In this case report, a 59-year-old woman presented with axial instability of plantaris tendon; post Achilles tendon lengthening. She beneficiated from a needle tenotomy of the PT and had a prompt symptom alleviation. The patient was fully satisfied and had a SANE score of 95% at 12 months follow up and was able to return to moderate sports activities without limitations (hiking, Nordic walking). The instability of the PT might be considered for the differential diagnosis of medial calf pain for which needle tenotomy may be considered a valuable option.

1. Introduction

Medial calf pain is mainly attributed to musculoskeletal disorders, especially medial gastrocnemius muscle tear. In most cases, treatment goals are achieved with a proper active exercise program.¹ In case of atypical clinical presentation or persistent symptoms, other etiologic factors for medial calf pain should be considered in the differential diagnosis, as Plantaris Tendon (PT) related pathologies (Fig. 1). The present case report describes PT axial instability as an etiology of persistent calf pain post-Achilles tendon lengthening. We defined “axial instability of the PT tendon” as a combination of axial translation of the PT tendon and discontinuity of the PT tendon with adjacent soft tissues. PT is considered for the differential diagnosis of Achilles or Calf pain, especially for ruptures and irritation of the Achilles Tendon.2, 3, 4 However, to the best of our knowledge, PT axial instability has never been reported.

Fig. 1.

Anatomical course of plantaris tendon in leg.

2. Report of the case

A 59-year-old female caregiver presented with left-sided hallux valgus and equinus due to gastrocnemius tightness. She needed a left Achilles tendon lengthening (Strayer procedure),⁵ and osteotomy of the first column (Maestro modified Scarf⁶ & Akin procedures⁷). Patient was satisfied with the forefoot surgery but, she complained of persistent sharp pain in the calf, which was triggered by physical activity such as ten running strides. This calf pain was absent before the surgery. The pain was precisely localized on the distal insertion of the medial gastrocnemius muscle. Since the surgery, the pain persisted despite active and passive physical therapies including soft tissue manipulations & active eccentric strengthening. Immobilization in a cast during 6 weeks was not successful too. In the 13 months following the surgery, there was no functional improvement, with a single assessment numeric evaluation (i.e., SANE score)⁸ of 60%. Active plantar flexion was painful. The posterior chain was flexible with a negative Slifverskiöld test.⁹ The patient had undergone Achilles tendon lengthening (Strayer procedure), and osteotomy of the first column (Maestro modified Scarf & Akin procedures) on the right side with an excellent outcome. Especially, the right calf was totally asymptomatic. Ultrasound evaluation of the left painful side demonstrated a thickened PT with heterogenous structure in the trajectory of the painful area (Fig. 2). During active contraction, the PT medially translated in the axial plane, creating a separation cavity between the medial gastrocnemius and soleus muscles (Fig. 3). The contralateral PT tendon was thin and stable on the axial plane during contraction. No adhesions or conjoint mobilizations were observed between the PT tendon and other adjacent structures. The patient wanted a minimally invasive procedure for pain relief. It was decided to cut the PT with a needling procedure, under ultrasound guidance, to solve the problem. Written informed consent was obtained from the patient for the publication of this case report and accompanying images.

Fig. 2.

Thickened and medially translated Plantaris tendon.

Fig. 3.

Plantaris tendon into the separation cavity before the needle tenotomy at rest (a) and medially translated into the axial plane during active contraction (b).

Under all aseptic precautions, local anesthesia and ultrasound guidance, (Samsung HS 60; 3–14 linear MHz probe) PT was sectioned using a 20G needle. The tip of the needle was slightly incurved, to allow a “fishing hook” effect on the PT during backward movements (Fig. 4). A complete tenotomy was achieved after 20 minutes of needling. At the end of the procedure, 40 mg of methylprednisolone was injected into the separation cavity for pain relief, in order to limit post-tenotomy inflammation. The dynamic medial translation of the PT between the medial gastrocnemius and the soleus muscles was no longer visible (Fig. 5). Three days after the procedure, active eccentric exercises were performed twice daily, as recommended by Alfredson et al.¹⁰ At 8 weeks follow-up, the patient presented only slight pain during exercise and recovered a running capacity of 20 minutes. This pain persisted during the entire follow-up, despite the application of a proper active eccentric rehabilitation protocol.¹⁰ A control ultrasound showed a gap between the proximal and distal stumps of the PT in the axial oblique plane (Fig. 6). A control MRI (Siemens Skyra 3T) with axial T1WI (weighted imaging) and three plans Dixon T2WI showed a discontinuity of the PT tendon with the thickened appearance of the stumps. The post-intervention persistent exercise-related pain could be explained by the presence of a classical “tennis leg” lesion, which was highlighted on the MRI performed at 6 months of follow-up. This MRI showed edema and partial detachment of the distal medial gastrocnemius muscle (Fig. 7), as well as the persistence of the fluid between the gastrocnemius and the soleus muscles, considered as the separation cavity (Fig. 8). At 12 months of follow-up, an ultrasound control showed a subtotal disappearance of the separation cavity (Fig. 9). Clinically, despite the persistence of the pain during running, the functional outcomes were considered good by the patient, with a SANE score of 90% at 6 months follow-up and 95% at 12 months of follow-up. The patient was able to perform moderate physical activity without pain or limitations like hiking and nordic walking (i.e. fast walking using 2 stocks to stimulate a moderate activity of the whole body musculature). She was fully satisfied with her condition.

Fig. 4.

20G needle with curved tip.

Fig. 5.

Plantaris tendon into the separation cavity at the end of the needle tenotomy at rest (a). The dynamic instability during active contraction disappeared (b).

Fig. 6.

Two months after the needle tenotomy, proximal and medial stumps of the plantaris tendon are seen in an axial oblique plan. The solution of continuity is highlighted by the arrow.

Fig. 7.

PT discontinuity (empty arrow) with the thickened stump on magnetic resonance imaging coronal view (a). Axial view showed intermuscular fluid (plan arrow) between the gastrocnemius and the soleus and edema (star) of the distal part of medial gastrocnemius (b).

Fig. 8.

At 6 months follow up, the magnetic resonance imaging showed similar lesions which were seen at 2 months. Coronal (a) and axial (b) views shows intermuscular fluid (plan arrow) and edema (star).

Fig. 9.

At 12 months, the ultrasound control showed a subtotal filling of the separation cavity (arrows), on either axial (a) and longitudinal (b) views.

3. Discussion

This case illustrates that PT instability can explain medial calf pain with the musculoskeletal pattern. Ultrasound-guided tenotomy of the PT allowed removing the conflict triggered by the instability. The functional outcomes were excellent.

PT partial or full tears, tendinopathy, and friction syndrome with Achilles tendon are well described.^3,11 We hypothesized that the PT axial instability created a separation cavity post Achilles lengthening (Strayer procedure). Orthopedic complication reported and known in the literature for the Strayer procedure are lesion of the sural nerve, persistent calves swelling, a change in the shape of the calf, complex regional pain syndrome, recurrence of the calf tightness or deformity, and wound infection, dehiscence or pain.^12,13 To the best of our knowledge, no complications involving directly the PT tendon were described.

Post-tenotomy radiological imaging at 2 & 6 months and excellent functional outcome at 1-year follow-up, showed that the axial instability resolved. However, partial avulsion of the medial gastrocnemius muscle was found on the imaging. This avulsion might have been triggered by local corticosteroid injection and by separation cavity which became overloaded once the patient resumed physical activity. The current case report showed a new pattern of PT pathology which was, successfully managed with a minimally invasive tenotomy. The tenotomy was performed under ultrasound guidance. A minimal invasive surgery procedure would also have been a feasible option, but the patient preferred to begin with a less-invasive procedure under ultrasound guidance first, and, in case of non-satisfactory outcome, to perform minimal-invasive surgery in a second time. The methylprednisolone infiltration could have alleviated the pain during the first few weeks, but not the axial instability. Therefore, in our view, methylprednisolone injection without percutaneous tenotomy would not have solved the problem.

However, some elements could be optimized for a future similar case. First, the needling tenotomy was quite fastidious and took about 20 minutes, because it was difficult to cut the tendon. It would have been easier and safer to cut the PT using a better technique and optimized material (e.g., hook knife),.¹⁴ Second, the steroid injection at the end of the procedure could have slowed the healing process of the medial gastrocnemius aponeurotic lesion, potentially explaining the persistence to the separation cavity. Finally, one can argue about the loss of the potential proprioceptive abilities of the PT.¹⁵ Despite this, the intervention presented here allowed a quick removal of the pain related to the instability of the PT.

In conclusion, the instability of the PT might be considered for the differential diagnosis of medial calf pain for which needle tenotomy of the PT is a valuable option.

Ethics approval and consent to participate

Ethics approval was taken from the ethical board (Vaud Ethical Board, Switzerland, decision#AO 2020–00006).

Consent for publication

Consent of the patient was obtained for publication of the data.

Availability of data and materials

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Funding

None.

Authors' contributions

AS: Writing the core of the manuscript; performing the US-guided intervention, approving the final version; ENP: Careful reading and substantial improvement of the manuscript, interpretation of the relevant imagery, approving the final version; JDN: Performing the initial surgery, careful reading and substantial improvement of the manuscript, approving the final version; AM: Reviewing the manuscript, careful reading and substantial improvement of the manuscript, approving the final version.

Declaration of competing interest

The authors declare that they have no competing interests.

Appendix A. Supplementary data

The following is the Supplementary data to this article: