1 Introduction

Anterior cruciate ligament (ACL) is one of the most commonly injured stabilisers of the knee joint, more so during sporting activities and direct trauma. The primary treatment modality of ACL tears is a reconstruction of the ligament so as to restore the stability and function of the knee joint. There are various autograft options available for the reconstruction of ACL. Autografts previously preferred were bone-patellar tendon-bone graft (BPTB), followed by hamstring tendons (HT) and Quadriceps tendon. BPTB grafts are associated with great bone to bone healing but started falling out of favour due to donor site morbidity.¹

Disagreements regarding the ideal graft for reconstruction continue to persist because of their disadvantages. Although there is greater mechanical strength and lower risk of donor site morbidity with HT graft, the variation in graft size from patient to patient is still a crucial aspect in determining the outcome because a smaller than ideal diameter of the harvested hamstring autografts can lead to graft failure.² Studies have shown that the height, weight and body mass index (BMI), are inexpensive yet helpful parameters for the surgeons to predict the tendon quality.³ As per the primary surgeon's observation, harvesting hamstring grafts for ACL in a case with a concomitant or pre-existing medial collateral ligament (MCL) injury, can be damaging to the MCL.

Use of Peroneus Longus Tendon autograft (PLT) is a relatively nascent development in the field of arthroscopic ACL reconstruction. Initially tested by using cadaveric PLT,⁴ it showed good results even when taken from a living donor.⁵ With more and more studies being carried out, the use of PLT as an autograft has been documented to hold various advantages such as good tensile strength and rapid regeneration at the harvest site.⁵ The ease of harvest, the apparent constancy of its thickness, and its mean thickness being similar to the native ACL make it an ideal alternative as an autograft.⁵ However, these studies call out for assessment at longer follow-ups and evaluation of donor site morbidity. In this study, we primarily evaluated the functional, clinical and radiological outcomes of ACL reconstruction performed using ipsilateral PLT as the autograft in the long term. Simultaneously, an assessment of the possible effects of PLT harvest on foot and ankle function was done to gauge the donor site morbidity.

We hypothesized that ACL reconstruction with a PLT autograft provides excellent functional, clinical and radiological outcomes in the long term, in addition to intra-operative consistency in terms of dimensions of the harvested graft and minimal long term donor site morbidity.

2 Material and methods

This longitudinal, prospective study was conducted over 113 consecutive patients who were operated on between January 2017 and November 2018 for an ACL reconstruction using PLT autograft. The study was conducted in accordance with the ethical standards of the responsible committee on human experimentation and with the Helsinki Declaration of 1975, as revised in 2008 (5). Informed written consent was taken and all the patients were explained in depth about the procedure. Patients' demographic data in the form of age, sex, BMI, and level of athleticism (non-athletic/recreational/amateur) were recorded. Patients with functional instability of the knee joint, Grade three laxity on the Anterior Drawer test and Lachman's test, Magnetic Resonance Imaging (MRI) reports suggestive of a complete ACL tear, arthroscopic confirmation of a complete ACL tear, no injury or previous surgery to the ipsilateral ankle, knee, or hip joint, normal foot arches, and isolated ACL tears were included in the study. Patients with partial thickness ACL tear, multiligament injury, concomitant meniscus injury, those undergoing revision ACL reconstruction surgery, professional athletes, and those diagnosed with a paralytic condition such as poliomyelitis or learning disability were excluded from the study.

Pre-operative Tegner-Lysholm⁶ and Foot and Ankle Disability Index (FADI)⁷ scoring were done for all patients. For acute ACL Injuries, patients were advised to wear a knee immobiliser and undergo physical therapy preoperatively, involving knee bending along with knee flexors and extensors strengthening exercises to attain a near-complete range of motion and symmetric quadriceps strength respectively, subsequently decreasing the joint effusion. Peroneal muscle activation exercises were also introduced. Once the inflammatory phase had resolved and ranges were regained at the knee joint, surgery was scheduled. The power of the study for calculating the selected sample size keeping the degree of freedom as two was calculated to be 99%. The STROBE checklist was followed while reporting of our study.⁸

2.1

2.1 Operative procedure

All patients were operated on under spinal anaesthesia. A diagnostic arthroscopic round was conducted and a complete tear of the ACL was confirmed.

Harvesting technique: Using a 2 cm incision on the posterior aspect of the lateral malleolus, the peroneal sheath was identified, isolated, and incised. The entire PLT tendon was then harvested using a tendon-stripper and it was then tripled (Fig. 1). No tenodesis was performed of the peroneus longus remnant to the peroneus brevis. The peroneal sheath was closed using absorbable sutures. The incision site was closed using non-absorbable sutures.

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Fig. 1 Peroneus longus tendon: A. Isolation B. Harvest C. Preparation.

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After sizing the tripled autograft, the femoral tunnel was drilled using the inside-out technique via the anteromedial portal and the tibial tunnel was drilled using the outside-in technique. Femoral fixation was done in all the patients using the tightrope endobutton and the tibial fixation was done using a biodegradable screw.

Post fixation, the laxity was checked arthroscopically by probing the ligament and clinically by the anterior drawer test. The patients with cartilage fraying were debrided using a shaver blade. Skin incisions and portals were closed with non-absorbable sutures.

Immediately post-operatively from day one, a fixed, short term physiotherapy regimen was followed for all the patients. These included:●Active assisted to active motion, as tolerated.●Passive extension exercises, heel press, leg hanging in prone position and active-assisted extension.●Passive flexion exercises.●Quadriceps strengthening exercises such as isometric quadriceps contraction, straight leg raises (SLR), controlled terminal knee extensions, concentric and eccentric contractions), hamstring strengthening.●Dorsiflexion and plantarflexion of the ankle, active toe movements, inversion and eversion movement).●Walker assisted walking with full weight-bearing.

Patients were followed-up on postoperative day 14 for suture line inspection and staples/suture removal. Reassessment parameters included checking the suture line, presence of any swelling or effusion, surrounding skin condition and range of movement of knee and ankle. The knee immobiliser was continued till good quadriceps control was achieved in terms of active SLR and dynamic quadriceps exercises without extensor lag. This was seen by approximately four weeks postoperatively. Patients were then assessed at regular intervals of follow-up. Functional assessment of the knee was done in a blinded manner by a single person using the Tegner-Lysholm knee score at six months, two years and three years postoperative follow-ups. Ankle morbidity was assessed using FADI and clinical assessment of the stability of the knee was using the Lachman test at the terminal follow up. All of the data was compiled on the SPSS 24 software and the improvement amongst the three follow-ups, the eventual functional outcome of the operated knee and donor ankle was calculated.

At the terminal follow-up, all the patients underwent an MRI evaluation. MRI evaluation of all the patients was done by a single-blinded expert radiologist who looked for the continuity of the graft, graft uptake using sound-to-noise quotient method,⁹ and also ruled out infection in all cases.

3 Results

A total of 113 patients (n = 113) were included in the study based on the inclusion criteria. 78 (69.03%) patients were males and 35 (30.97%) patients were females. The mean age of the study population was 26.22士5.76 years (Range:17–39 years). The mean BMI was 28.07 ± 4.42 kg/m² (Range: 20–38 kg/m²), with 31 (27.43%) patients in the healthy, and 41 (36.28%) patients each in the overweight and obese category.

Preoperatively patients were given the Tegner-Lysholm questionnaires and their mean score was 41.12 ± 8.5. The pre-operative mean FADI was recorded as 97.56 ± 2.64. Surgery was performed on 65 (57.52%) right and 48 (42.48%) left knees.

All the patients underwent the same management protocols in terms of surgery and rehabilitation. Intraoperatively, the mean length of the PLT before tripling was found to be 27.07 ± 2.76 cms (Range: 21–32 cms) and the mean thickness on tripling the graft was 9 ± 0.71 mm (Range: 8–10.5 mm). Based on the distribution with respect to BMI, no significant difference was noted in the mean thickness of the PLT graft on tripling between the healthy, overweight and the obese group (8.95 ± 0.72 vs 9 ± 0.68 vs 9.04 ± 0.74 mm) as seen on applying the Pearson correlation coefficient (p value = 0.834). (Table 1).

The mean Tegner-Lysholm knee score at 6 months, 1 year, 2 years, and 3 years follow up was 89.86 ± 3.31, 90.98 ± 2.58, 91.46 ± 2.66, 92.21 ± 2.57 respectively showing improvement in the scores with every follow up on repeated measure Freidman test, albeit statistically insignificant (p > 0.05). According to the Tegner-Lysholm stratification criteria at the terminal follow-up, 101 (89.38%) patients fell into the excellent (>90) category, with no detrimental effect of the surgery on their levels of activity or frequency of participation in sporting activity. 12 (10.62%) patients fell into the good category (84–90) with normal/near normal knee function. There was no flexion contracture at the end of six months, one year, two years or three years follow up, and the patients regained functional ranges of motion (Fig. 2). Excellent cosmesis of the healed suture line at both, the donor and recipient sites were found.

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Fig. 2 Images of case number 48 showing A. Preoperative T1 weighted MRI in sagittal view showing buckled PCL and completely torn ACL B. 3-year postoperative follow-up with 120° flexion C. 3-year postoperative follow-up with full extension D. 3-year postoperative T1 weighted MRI in sagittal view showing good healing of the graft.

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Ligament stability was assessed using the Lachman test at terminal follow-up. We were able to verify normal anteroposterior laxity in 102 patients (90.27%) while 11 patients (9.73%) had 1+ laxity. None of the patients had 2+ or 3+ laxity on Lachman's test. At 3 years postoperatively, neither crepitation nor pain was identified in the patellofemoral joint in any patient.

At three years postoperatively, follow up MRI was conducted for all the patients. MRI showed good uptake of the graft at the surgical site based on sound-to-noise quotient (Fig. 3). Also, patients were evaluated sequentially for the donor site morbidity by FADI with the mean FADI coming to 94.84 ± 3 at three-year follow-up as compared to 97.56 ± 2.64 which was noted to be statistically insignificant on using Wilcoxon signed-rank test (p value > 0.05). According to the FADI assessment, no patient exhibited any degree of impairment in sporting activities or any kind of dysfunction at the ankle joint. 106 (93.81%) patients reported no complaints of any kind at the donor site, however seven (6.19%) patients complained of light to moderate pressure pain and paraesthesia in the region of the harvested PLT.

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Fig. 3 Sagittal view of T2 weighted MRI for Case number 14 A Preoperatively showing buckled PCL and complete ACL tear B 3-year postoperative showing good graft uptake.

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4 Discussion

ACL reconstruction is one of the commonest procedures in orthopaedics, done to functionally restore the role of the native ACL along with its ultimate tensile load of 2020 ± 264 N. With multiple graft options available, the debate about the preferred graft option rambles on. Autografts have shown to give comparable, if not better results that allografts, as demonstrated by D'Ambrosi et al.¹⁰ Autografts such as HT and the BPTB graft remain the forerunners due to minimal reaction rates and preclusion of disease transmission.¹¹ Irrespective of the graft used, the most crucial preoperative consideration is to provide optimal knee stability and minimise the incidence of re-rupture.

The BPTB graft was once considered a gold standard for ACL reconstruction due to its biomechanical strength (ultimate tensile load of 2300 N), graft size consistency, ease of harvest and the inherent bone-to-bone healing within the two tunnels.¹² However, complications such as quadriceps weakness, extensor lag, patellar tendon rupture, patellar/tibial fracture, anterior knee pain, difficulty in kneeling, and the feeling of numbness following any kind of injury to the infra-patellar branch of the saphenous nerve reduced its popularity.¹³

Quadrupled HT grafts have greater biomechanical strength (ultimate tensile load of 4090 ± 265 N) and lesser incidence of patellofemoral pain and extension loss than a BPTB graft. However, using the HT can significantly alter the strength of the hamstring muscle group as shown by Vertullo et al.¹⁴ The role of hamstrings in safeguarding the anterior translation of the tibia by counteracting the quadriceps action is crucial for the success of an ACL reconstruction, in addition to compromising on the active flexion of the knee joint. Inadequate diameter or thickness of HT graft plays an important role in failure rates.^15,16

A systematic review of the current literature published by Conte et al. found 6.8 times the greater relative risk for graft failures when a graft (irrespective of the donor site) was thinner than eight mm.³ Accordingly, in our study, the mean PLT autograft diameter on tripling was 9 ± 0.71 mm with the lowest thickness being eight mm. Similarly, a minimum length of 21 cm has been ascertained while fixing the femoral end with an endobutton which was in congruence with our mean graft length before tripling of 27.07 ± 2.76 cms with the range of 21–32 cms.

Anthropometric data like height, weight, and BMI have been shown to predict the graft size of the patient, thereby helping surgeons to pre-plan alternative graft options.¹⁷ In our study, the mean BMI of the patients was found to be 28.07 ± 4.42 kg/m² and it had no statistical correlation with the graft size. The use of PLT autograft is a recent development in ACL reconstruction. The advantages are its high tensile strength (single strand: 1950 N; double-strand: 4268 ± 285 N), its mean thickness being nearly the same as that of the native ACL and its ease of harvest.^18,19

Various drilling options have also been documented for tunnel positioning, namely anteromedial and transtibial. Loucas et al., in 2021 showed superior results with anteromedial drilling as compared to the latter. The same method was followed in our study.²⁰ It is also understood that in twisting injuries to the knee if the MCL is injured, there is a fair chance of damaging the MCL further at the time of HT graft harvest. To avoid that, peroneus longus can be a good substitute.

The results of this study were comparable to that of Kerimoglu et al.,⁵ and Budhiparama et al.²¹ Good joint stability was obtained despite no anterolateral ligament reconstruction.²² At the terminal follow-up, 101 (89.38%) patients had Tegner-Lysholm scores in the excellent category (95–100) and 12 (10.62%) patients in the good category (84–94).²³ There was no ankle dysfunction related to the donor site morbidity, suggested by the excellent mean FADI score (94.84 ± 3) at the terminal follow up of the patients. The athletic population of the study returned to their pre-surgery activity level, without any compromise in ankle strength, the strength of eversion or gait-related complaints, despite no tenodesis of the peroneus longus stump to the peroneus brevis. This is presumptively due to the good regeneration potential of the harvested full-thickness PLT. This finding was in tandem with the findings of Joshi et al. wherein resection of the PLT showed no major influence on the ankle joint either.¹⁹ This is primarily down to the finding of Rhatomy et al. wherein peroneus brevis was concluded to be the more effective evertor of the ankle joint.²⁴ There was no effect of PLT harvest on arches of the foot. The clinical stability of the knee joints was also excellent, with over 90% of patients having no anteroposterior laxity at the terminal follow-up, as was the case in the study published by Joshi et al.¹⁹

Although statistical evidence in favour of using PLT as an autograft for ACL reconstruction in athletic as well as the non-athletic population was found in our study, the authors recognise certain limitations of the study such as a restricted geographical area from where the patients were assessed, and the lack of a control group. As the MRI evaluation and the assessment of functional outcome was done by a single blinded radiologist, there is potential for human error. Similarly, more studies with a larger sample size, a longer follow-up period, and the effect of PLT graft in ACL tears with concomitant ligamentous or meniscal injuries can help in fortifying the findings of this study.

5 Conclusion

Peroneus longus tendon has a constant and dependable thickness and length of harvest. Functional outcomes in patients undergoing ACL reconstruction with PLT as the autograft showed excellent clinical, functional, and radiological results with no donor site morbidity even at a follow-up of 3 years.

Disclosure of potential conflicts of interest

The authors declare that they have no competing interests.

Financial disclosure

None of the authors received any kind of funding for this research.

Informed consent

Informed consent was obtained from all individual participants included in the study.

Ethics approval and consent to participate

All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation and with the Helsinki Declaration of 1975, as revised in 2008 (5).

Author contributions

Amyn Rajani: Conceptualization, Methodology, Supervision, Writing-Review and Editing Urvil Shah: Investigation, Data curation, Validation, Writing-Original draft Anmol Mittal: Investigation, Data curation, Validation, Writing-Original draft Alisha Rajani Investigation, Resources, Writing-Review and Editing Meenakshi Punamiya: Writing-Review and Editing, Project administration Richa Singhal: Software, Formal analysis, Writing-Review and Editing.