Similar to conservative treatment, percutaneous suturing of the Achilles tendon does not accurately restore the anatomical position of damaged fibers or guarantee the appropriate repositioning of the stumps remaining after tendon rupture [1, 3, 10]. On the other hand, with the remaining hematoma and primary regenerative local response serving as a foundation, function may be restored . It is worth emphasizing that this is not the case with "open" sewing, during which the hematoma is flushed out and the effects of the immediate repair mechanisms are eliminated . The fibers become aligned during the scar remodeling phase, i.e., at the beginning of resistance training, especially when the limb is loaded.
Excessive use of the operated limb leads to stretching of the soft connections between the stitched tendon stumps, which may result in secondary defense responses such as swelling along the Achilles tendon. According to the interviews, none of the subjects with DRC closely followed the recommendations of the physiotherapists. This low level of adherence mainly manifested in levels of daily and professional activity significantly exceeding the level that was recommended. The presence of deformities was statistically significantly associated with chronic pain having occurred before the rupture of the Achilles tendon. This finding indicates the presence of chronic tendinopathy and severe degenerative changes in the tendon. Apart from tendinopathy, the patient's weight may be important in the development of deformation. People with current DRC had a significantly higher body mass index than did those without DRC (30.3±1.7 vs. 27.3±2.9). However, these two groups did not differ in terms of the other parameters analyzed. In summary, the following important factors can lead to the deformation of the shape of the scar after surgery: a lack of full control of stump repositioning; chronic tendinopathy accompanied by degenerative changes and swelling of the Achilles tendon during overlapping, excessive, premature loading of the muscular-tendon unit and stretching; and excessive body weight.
Calf nerve injury is one of the complications of both open and percutaneous surgery . It should be noted that intraoperative calf nerve damage occurs immediately after surgery, and sensory recovery in the nerve supply zone (if it occurs) is a slow process and can take approximately 6 months . None of the operated patients reported sensory disturbances or other complaints in the area of its supply within 4 weeks after the surgery, during the period of no weight-bearing, during the use of the orthosis, or during the initial phase of rehabilitation. Therefore, the sensory disturbances in the calf nerve supply that occurred in 4 patients were not associated with intraoperative damage. The occurrence of symptoms was noted within 4–6 weeks after surgery, when the rehabilitated patients began to gradually load the operated limb with body weight.
MAS was observed in 11.1% of the subjects and was significantly associated with the occurrence of pain before the rupture of the Achilles tendon, suggesting the presence of tendinopathy. MAS concomitant with DRC was also found in the study population. Symptoms of ankle stiffness occurred in 4 out of 6 subjects with DRC. This deformation can weaken the elastomeric properties of the tendon and prevent it from moving smoothly. Percutaneous surgery allows the existing sliding tendon to be preserved . Moreover, this type of surgery very rarely leads to adhesions around the tendon that can limit its mobility relative to the surrounding tissues.
OST occurred in 3 out of 4 subjects with SNI symptoms but did not occur among those who did not report SNI. It has been suggested that secondary defensive reactions in the form of edema along the Achilles tendon may cause pressure on the nerve at the point of contact with the tendon . Symptoms of nerve dysfunction without soft tissue edema occurred in only one subject. This subject was the woman with the highest BMI in the whole group (33.1 kg/m2). The BMI value did not differ significantly with regard to the occurrence of SNI symptoms, but it could have been a predisposing factor for this symptom due to soft tissue overload in the operated zone.
Local tissue irritation associated with suture knots is caused by a defensive biological response to the foreign body, despite the total biocompatibility of the material used for sewing. The presence of internally palpable surgical thread nodes is a well-documented observation in percutaneous and open procedures . However, this symptom has occurred incidentally in studies by other authors, and the removal of excess suture knots in another operation leads to its resolution .
The occurrence of side effects and complications may be associated with the type of rehabilitation method used after Achilles tendon injury. In recent years, an acceptable approach for the rehabilitation of Achilles tendon rupture has been identified, and the approach promotes immobilization with an orthosis, as well as early loading of the operated limb with limited ankle movement .
Rehabilitation progression and the impact of side effects on rehabilitation treatment
Rehabilitation after surgery within the heel tendon is a complex process for which no commonly accepted protocol has yet been developed . Whether early full weight-bearing of the limb (within 1–2 weeks after surgery) should be permitted is an aspect of the protocol that has been debated [18, 31].
In this study, patients were not allowed to load the operated limb with body weight for the first 2 weeks. Additionally, active dorsiflexion and plantar flexion of the ankle and circular movements of the foot were introduced gradually at 2 weeks after the surgery. An important element of rehabilitation after Achilles tendon rupture is finding a "golden mean" between a period of immobilization that is too long and leads to many undesirable effects and one that is too short and can lead to secondary rupture of the tendon . Maqurrian  believes that the rehabilitation protocol should take into account the surgical technique, in particular the type of suture used to connect the stumps of the ruptured tendon. Clanton et al.  noted that minimally invasive techniques for percutaneous repair is more likely to cause the tendon to stretch than is open treatment. The authors also suggest that percutaneous repair is associated with a risk of insufficient tendon capture. Ultimately, however, no significant differences in the strength of the tendon between the techniques used were found (open repair, the Achillon Achilles Tendon Suture System, the PARS Achilles Jig System and the Achilles Midsubstance Speed Bridge Repair variation) .
A high percentage of tendon rerupture (10%) after percutaneous sewing was observed in a study by Maes et al. . The authors explained that these results were caused by allowing weight-bearing on the operated limb too early.
Lee et al.  analyzed the strength of three types of anastomoses: Krackow, reinforced Krackow and percutaneous anastomosis. The tendons were subjected to repeated and increasing loads (100, 190 and 369 N). Based on the results of these experiments, Lee et al.  do not recommend protocols introducing early full weight-bearing and early ankle movements.
The time at which resistance exercises and dynamic training should be introduced is also debatable. According to the rehabilitation protocol proposed by Gwynne-Jones et al.  and Doral et al. , resistance exercises should start after week 6; however, according to the program used in this study, they were started earlier, at an average of approximately 5 weeks after surgery (5, 1±1,5). For dynamic training, the abovementioned authors started this training as early as 10 weeks after surgery, while in this study, dynamic training began no sooner than 12 weeks postoperatively, after the following criteria were met: the subject was able to perform a single-toe raise on the operated limb and was able to walk independently and symmetrically.
Objective and subjective results of treatment
The Achilles tendon total rupture score (ATRS)  is a commonly used point scale for the subjective evaluation of the results of the treatment of complete Achilles tendon rupture, movement restrictions and their impact on physical activity .
While dynamometric muscle measurements are often used as indicators of tendon recovery after injury [37, 38], there are no reports on the use of stability or proprioception indicators for this purpose. In this work, three stability indicators (APSI, MLSI, OSI) were assessed. The obtained OSI results may indicate an improvement in deep sensation and proprioception in response to ongoing rehabilitation activities. This information is valuable because deep sensation disorders are considered one of the elements that is most difficult to restore to the preinjury state . In turn, proprioception disorders are considered a predisposing factor for tendon damage in general . In summary, the lack of significant differences in the OSI values between the OP and NOP limbs after rehabilitation treatment may indicate an improvement in deep sensation. On the other hand, from the beginning of dynamic training to the end of rehabilitation, there was no significant reduction in the OSI value on the operated side or on the healthy side.
In the study presented here, as in another publication , the strength of the planar flexor and dorsiflexor muscles was measured under isokinetic conditions at a speed of 60°/s. In both cases, no significant differences were observed in the maximum muscular strength of the dorsiflexors at the end of the rehabilitation period. Significantly lower values of strength were found, however, in the plantar flexors on the operated limb at the end of rehabilitation (on average 164 days from surgery) in this study and one year after surgery in the study by Syrek et al. .
The amount of data on the direct impact of postoperative complications on functional results is very limited. Therefore, one of the aims of this study was to investigate whether side effects slow rehabilitation. If so, we aimed to determine whether this effect translates into measurable changes in the objective parameters. To answer this question, we aimed to determine the impact of side effects on the heel lift height relative to the ground, stability indexes, and the isokinetic strength of the plantar flexors and dorsiflexors of the ankle. Multifactorial analysis showed a significant influence of all side effects, i.e., DRC, SNI, MAS and OST, on objective indicators.
DRC and MAS had a negative effect on the heel lift height, but this effect was observed only in the second examination (at the end of rehabilitation), while OST caused the OSI to worsen in both examinations. SNI had a similar effect on the difference in the heel lift height of the NOP and OP limbs in both studies. This symptom was associated with a worse OSI in both the first and second examinations.
The deficit in the muscular strength of the plantar flexors of the foot was not affected by the other side effects observed in the course of rehabilitation, i.e., DRC, MAS, and OST. The above symptoms slowed the course of rehabilitation, but there are no indications that they might decrease the muscular strength of the operated limb.
Side effects had a significant adverse effect on the heel lift height difference between the healthy and operated sides. Given that there is a correlation between isokinetic muscle strength and the heel lift endurance test result, a relationship of these symptoms with muscle strength should be expected. It has been suggested that a decrease in the heel lift height may be associated with the weakening of the muscles and/or lengthening of the operated tendon, but this relationship needs to be studied further .
A comprehensive analysis of the impact of multiple factors on spontaneous, subcutaneous, and complete heel tendon ruptures was proposed in a literature review, and considering our study, there is ongoing research on the optimal and permanent recovery of the function of the damaged area and improvement in the general physical condition of the people undergoing treatment.
Achilles tendon ruptures are more common in people who lead a sedentary lifestyle and take part in physically demanding activities in a sporadic and unprepared manner . A way to reduce the number of Achilles tendon ruptures could be to inform individuals who are interested of the need for a gradual, appropriate increase in the level of physical activity and to be conscious of the dangers arising from sudden, rapid increases in the intensity of physical activity without proper preparation .