Introduction

The anterior cruciate ligament (ACL) is the most frequently injured structure in the knee, accounting for 86.5% of knee injuries [1]. Multiple studies have established the crucial role that the ACL plays in knee alignment, stability and kinematics. If not appropriately restored, its deficiency can lead to early degenerative changes in the knee joint [2].

Arthroscopic ACL reconstruction is the mainstay of treatment of ACL tears, for which a wide array of autografts and allografts has been employed. Though the ongoing debate of hamstring-tendon graft versus bone-patellar-bone-tendon graft persists to be the most popular, recent studies adopting the use of the peroneus longus tendon autograft in ACL reconstruction have surfaced showing promising functional outcomes in the knee. Its thickness, high tensile strength and ease of harvesting make it an ideal graft [3, 4]..

While prior studies have primarily focused on surgical outcomes for the knee, few have considered the possibility of donor-site morbidity at the ankle, and even fewer have evaluated the same in the Indian community [5,6,7,8,9,10,11,12,13,14,15].. The purpose of this study was to assess whether harvesting the ipsilateral peroneus longus tendon for ACL reconstruction causes donor-site morbidity at the ankle.

Materials and Methods

This was a prospective longitudinal study conducted from July 2019 to September 2021 at a tertiary care hospital in South India after approval from the Institutional ethics committee. Adults above the age of 18 years diagnosed to have an ACL injury based on clinical assessment and confirmed on magnetic resonance imaging undergoing arthroscopic ACL reconstruction with peroneus longus tendon autograft at our institution were included after providing their written informed consent. Patients with ligament laxity, inflammatory ankle pathologies, osteoarticular disease of the ankle, prior ankle injuries or surgery around either ankle were excluded.

Surgical technique

All patients were operated upon at a single centre by two surgeons from the same department after standardising the protocol for harvesting the graft. Surgeries were performed under spinal anaesthesia in supine position with a high pneumatic tourniquet applied to the ACL-deficient limb. The lower portion of the table was dismantled and the affected limb left to dangle with the knee flexed to 90° with a well-padded lateral post for support. A well-leg support was used for the opposite side, and the ACL-deficient limb was painted and draped. After exsanguinating the limb with an Esmarch bandage, tourniquet pressures were maintained at 300 mmHg for a time no longer than 100 min. A conventional diagnostic arthroscopy confirmed the presence of a torn ACL and any other associated injuries.

The patient’s ankle was exposed and peroneus longus tendon palpated subcutaneously. A 3cm longitudinal skin incision was made behind the lateral malleolus with a No. 22 blade to expose the peroneus longus and brevis within their tendon sheath (Fig. 1a). The sheath was then incised longitudinally with a No. 10 blade and the peroneus longus tendon identified and isolated with a right-angled forceps (Fig. 1b). Using Ethibond 1–0, the tendon was tagged and cut distally leaving a 1cm stump (Fig. 1c). A tendon stripper was used to separate the peroneus longus tendon at its musculotendinous junction which was then retrieved through the incision (Fig. 1d). The distal stump of the peroneus longus was sutured to the peroneus brevis using Ethibond 1–0 in interrupted sutures and the peroneal sheath was closed using Vicryl 2–0 interrupted sutures (Fig. 1e). A compression dressing was applied to the ankle which was then changed to a water-resistant adhesive dressing on the second post-operative day. Suture removal was done on the eleventh post-operative day.

Fig. 1
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a–e Operative technique for harvesting peroneus longus from the ipsilateral ankle

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Rehabilitation

All patients had a post-operative physiotherapy assessment and were provided with a printed pictographic protocol for home-based ankle rehabilitation aimed at evertor strengthening and obtaining good range of motion at the ankle and subtalar joints (Annexure 1). The protocol with exercises was explained to patients during follow-up visits and implemented in a timely fashion with increasing difficulty.

Functional outcomes of the ankle joint

Patients were followed up at one, three and six months from their date of surgery. Foot and Ankle Score (AOFAS) and Karlsson–Peterson scoring systems were used for subjective functional assessment of the ankle preoperatively and during all follow-up visits. Invertor and evertor strength were assessed using Chatillon MSE-100-M hand-held dynamometer (Fig. 2) by a single investigator at 1, 3 and 6 months following surgery and compared to the normal side. Static and dynamic plantar pressure measurements were done on those patients willing for the same at 3- and 6-month of follow-up, comparing findings of the operated limb to that of the normal side using a Diers Pedoscan Plantar Pressure Measurement System.

Fig. 2
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Chatillon MSE-100-M hand-held dynamometer

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The data were analysed using descriptive statistics with the aid of SPSS version 28 and Microsoft Excel 2022. The quantitative data were reported in terms of mean and standard deviation, and significance was determined using the student's t test and analysis of variance (ANOVA). To investigate group differences, subsets of data were subjected to post hoc analyses. A p-value < 0.05 was considered statistically significant.

Results

Our study consisted of 20 patients with a mean age of 32.75 ± 10.53 (19–56) years operated upon at a mean of 6.85 ± 9.76 (0.5–36) months following injury. We noticed a male predominance of 70% among participants and that the left knee (60%) was more frequently affected than the right. Most patients sustained injuries from sport (45%) followed by falls (40%) and road traffic accidents (15%).

Ankle scores

Table 1 shows the mean AOFAS and Karlsson–Peterson ankle scores prior to surgery till 6 months of follow-up with Fig. 3 showing trend in the two scores between pre-op and follow-up. Post hoc analysis of the same is shown in Table 2 with gradual improvement in ankle function and no significant difference between pre-operative scores and scores at 6 months of follow-up.

Table 1 Mean AOFAS and Karlsson–Peterson scores (n = 2)
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Fig. 3
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Trend in mean AOFAS and Karlsson–Peterson (KP) score from pre-op to 6 months follow up

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Table 2 Post hoc analysis of mean AOFAS and Karlsson–Peterson scores
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Ankle strength

While invertor strength was not significantly impaired, dynamometric findings showed significant impairment of eversion in the operated ankle compared to the normal side (Table 3). Post hoc analysis showed significant short-term improvement in strength of both eversion and inversion (Table 4), and the same trend can be observed in Figs. 4, 5, respectively.

Table 3 Mean strength of eversion and inversion of the peroneus-deficient and normal sides (n = 20)
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Table 4 Post hoc analysis of mean strength of eversion and inversion of the peroneus-deficient foot
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Fig. 4
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Trend in mean strength of eversion of operated and normal sides during follow-up (n = 20)

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Fig. 5
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Trend in mean strength of inversion of operated and normal sides during follow-up (n = 20)

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Pedobarography

Among the 20 participants, 7 agreed to undergo static and dynamic plantar pressure analysis as detailed in Tables 5 and 6, respectively.

Table 5 Static plantar pressure parameter measurements of operated & normal foot at 3- and 6-month follow-up (n = 7)
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Table 6 Dynamic plantar pressure parameter measurements of operated & normal foot at 3- and 6-month follow-up (n = 7)
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At 3 months of follow-up, the mean average plantar pressure, foot axis angle, maximum plantar pressure, plantar surface area, weight distribution and hindfoot weight distribution during static pedobarography were found to be higher on the normal side compared to that of the operated limb. Among these, the differences in plantar surface area and hindfoot weight distribution were found to be statistically significant. By 6 months of follow-up, there was no significant difference in any parameter between the normal and operated sides.

During dynamic pedobarography, the average plantar pressure, maximum plantar pressure, step duration, surface area and weight distribution at 3 months of follow-up were found to be higher on the normal side. The difference in average pressure was the only one that was statistically significant, which then normalised by 6 months of follow-up. The plantar surface area on the operated side significantly increased on the operated side at 6 months of follow-up (p = 0.037).

Among these seven patients, five (71.4%) produced an abnormal pattern in their dynamic pedobarographic on the peroneus-deficient side (Fig. 6). We noticed a deviation of the point of maximum pressure away from the medial aspect of the forefoot to a point much lateral to the centre of pressure trace. Two patients showed these features at 3 months, two at 6 months and one at both 3 and 6 months of follow-up.

Fig. 6
figure 6

Dynamic pedobarographic findings at 3-months after harvesting the right peroneus longus tendon autograft (a) and left peroneus longus tendon autograft (b). The black circle denotes the point of maximum pressure and has shifted lateral to the centre of pressure (COP) trace

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Discussion

The peroneus longus tendon is an attractive autograft option for ACL reconstruction with its ease of harvesting, predictable size, tensile strength and good functional outcomes as evidenced by pre-existing literature [3, 4, 10, 11, 14, 16,17,18,19,20,21]. Our findings suggest that while this procedure results in good subjective outcomes as perceived by patients, there is objective evidence suggestive of donor-site morbidity. The combination of evertor weakness alongside with the dynamic pedobarographic findings of redistributed plantar pressure to a point more lateral can be explained by the deficiency of peroneus longus in these subjects.

The peroneus longus not only plays a role in first-ray plantar flexion and eversion, but also maintains the transverse arch and medial longitudinal arch. It contributes to the stability of the ankle whilst acting in equilibrium with other muscles [22]. Manik et al. highlighted the possible compensatory role of other leg muscles in case of removal of the peroneus longus. They also mentioned that while ankle instability is associated with decreased evertor strength, a modest decrease may not have as drastic an impact [22].

Kerimoglu et al. found good knee function after using the peroneus longus and deemed it a suitable autograft in ACL reconstruction to circumvent morbidity from harvesting hamstrings. Their assessment of the donor site however, was subjective and based on symptoms reported by patients [23]. Various studies have relied on subjective scoring systems that have shown good results during short-term follow-up much like our study [3, 10, 11, 13, 14, 19,20,21, 24].

Fermin et al. concluded that while the peroneus longus autograft is adequate in its dimensions and outcomes, that non-validated tools and questionnaires provide favourable outcomes of donor-site morbidity. Stronger evidence using validated tools is required to justify its routine use [25].

Rhatomy et al. have studied the use of peroneus longus and have demonstrated the potential of the tendon to regenerate on MRI [9, 13, 18, 24]. They used subjective questionnaires and a hydraulic dynamometer for strength testing, but unlike our study, did not find a significant difference between the two sides [26].

While Angthong et al. saw good knee function with minimal deterioration in AOFAS and VAS-FA scores post operatively, they found laxity in 8.4% of patients. They noticed deterioration of eversion, inversion, and first-ray plantar flexion on isokinetic testing with one patient developing ankle instability and therefore could not recommend peroneus longus as an autograft for ACL reconstruction [27]. Studies by Shi et al. and Nazem et al. used a robotic dynamometer and Kistler force plate respectively and reported no short-term evidence of donor-site morbidity [4, 28].

Our literature review failed to uncover any previous study that used pedobarographic data in analysing peroneus longus-deficient ankles. Mineta et al. conducted a study on 22 athletes with ankle instability following lateral ankle sprains and noticed increased lateral loading during a single-leg balance test. They correlated this with decreased peroneus longus activity and recommended that rehabilitation should include specific muscle activation training [29]. Though our patients were not made to perform single-leg balance tests, the findings described by the author were comparable to the dynamic changes seen in our study while making patients walk.

Despite how common and frequently used peroneus longus has become as an autograft in ACL reconstruction, there are very few tools to objectively assess the effects on the ankle. Our study is unique as it provides insight into the merit of pedobarographs as a tool for assessing the donor ankle. According to our literature review, no previous study has employed pedobarographic data as an objective tool for assessing donor ankles following the harvest of peroneus longus. The limitations of this study were the small sample size, short duration of follow-up and while strength testing was done by a single examiner, the use of a hand-held dynamometer is prone to poor intra-examiner reliability. We did not have access to an isokinetic dynamometer and were unable to perform gait analysis on these patients which would have.

Conclusion

While the use of peroneus longus tendon autografts in arthroscopic ACL reconstruction does not seem problematic on short-term subjective assessment, there is objective evidence in keeping with evertor weakness, weakness of first-ray plantar flexion and possible ankle instability.

Peroneus longus tendon is a viable option in selected patients who acknowledge the need for compliance with physiotherapy and are committed to rehabilitative efforts. Plantar pressure studies at regular intervals of follow-up can determine compliance to physiotherapy, need for aggressive rehabilitation and the presence of ankle instability. Further research with pedobarography is necessary to evaluate long-term donor-site morbidity and the possible effects on ankle stability independent of subjective questionnaires.