Plantar plate radiofrequency and Weil osteotomy for subtle metatarsophalangeal joint instablity

In the last decade, we observed a crescent interest in the lesser toe deformities, particularly metatarsophalangeal (MTP) joint instability [1‐5]. Recently, the involvement and importance of the plantar plate (PP) in lesser MTP joint instability has been evaluated and classified [6]. In the same way, grading schemes describing MTP joint instability have been reported [7, 8]. The main purposes of these grading systems are to address the pathophysiology of the lesions and to stratify different stages of soft tissue involvement, in order to try and create a treatment algorithm with alternatives for each different stage of MTP plantar plate lesion.

Until now, there has been no current treatment available in the literature to address the initial instability of the MTP joint. All reports describe the treatment for more extensive lesions with a clear clinical presentation without stratifying the grade of joint involvement [3, 8‐10]. For the early stages of lesser MTP joint instability, conservative management is recommended with toe taping or corticoid injection, but these methods cannot prevent deformity progression [6, 11].

Electro-thermal capsular shrinkage (ECS) has become a common procedure for a variety of joint conditions usually associated with instability [12]. It is well known that radiofrequency in supra-physiological temperatures results in active wound healing by triggering the cellular response [13‐17]. Based on these findings, we hypothesized that radiofrequency could affect the injured plantar plate in the early stages of MTP instability, preventing the progression of deformity.

The aim of this prospective study was to show the results obtained in the treatment of a group of patients with subtle plantar plate pathology with the arthroscopic radiofrequency shrinkage and sealing of the lesions combined with Weil metatarsal osteotomy.

Seventy-three percent of our patients were females with a mean age of 59 years. Most of them had a history of wearing high-heeled shoes (63 %) and only some reported sport activities (26 %). Bilateral involvement was more common than single appearance and our average follow-up was 20 months ranging from 12 to 47 months.

Table 1 reports the data regarding the number of affected joints. Sixty-five percent were grade 0 of the anatomical classification of plantar plate tear with a greater predilection for the third metatarsophalangeal joint. However, among the joints that were classified as grade 1, 58 % affected the second MTP joint. Sixty percent of the joints were considered acutely painful and 63 % demonstrated increase of the interdigital space.

Table 2 demonstrates the statistically significant difference between pre- and post-operative AOFAS scores (p < 0.0001), with an average increase of 34.5 points in the total sample. There was no statistically significant difference between the grades 0 and 1 in the AOFAS score average changes (p = 0.9842). For the VAS score, a statistically significant difference was observed between pre- and post-operative analysis (p < 0.0001), with a mean reduction of 6.9 in the total sample. Post-operative analyses of the VAS resulted in a statistically significant difference between grades 0 and 1 (p = 0.0340).

Table 3 presents the analysis of toe elevation and toe purchase. The grade 0 lesion showed a positive toe purchase, significantly higher than grade 1. It is interesting to demonstrate that 80 % of our patients had a positive toe purchase after surgery and more than 94 % of them had no toe elevation post-operatively. The individual analysis of the grades 0 and 1 regarding elevation showed a statistically significant result between the pre- and post-operative period with p values <0.0001 and <0.0016, respectively. However, no statistically significant difference between the groups was observed for the presence of elevation in the final evaluation (p = 0.1109). The toe purchase result was statistically significant. The grade 0 group showed more joints with toe purchase positive than grade 1 group. The individual and comparative analysis of the groups presented a statistically significantly different data (Table 3).

Table 4 demonstrates an important finding regarding the stability graduation. In the pre-operative period, 97 % of joints were classified as grade 1 of drawer test instability (<50 % subluxable). However, in the post-operative evaluation, more than 82 % of the joints were completely stable (grade 0 of instability). The individual improvement of the stability was statistically significant. In grade 0, 87 % of the joints became stable in the post-operative analysis (p = 0.0001) and in grade 1, 83 % of the joints improved in the pre-operative level of instability (p = 0.0139). The comparative analysis between the groups was not statistically significant.

Most of the joints were congruent in the pre-operative radiographic measurements (71 %) and we correlate these data to less extensive tears that our patients presented. The post-operative analysis demonstrates that less than 3 % of the joints had incongruent radiographic relations. The individual analysis of the groups was statistically significant (grade 0, p = 0.0253; grade 1, p = 0.0455) and the comparative analyses were not (p = 0.3430).

Currently, it is known that the plantar plate plays an important role in the stabilization of the lesser metatarsophalangeal joints. Recent biomechanical studies have shown that PP was the main isolated stabilizer of the MTP joints in the dorsal–plantar direction [4]. Deland and Sung [20] showed how an isolated repair of the collateral ligaments was insufficient to resolve instability resulting from PP deformity, which may indicate that the PP itself has a crucial role in stabilizing the joint.

In recent cadaveric dissections of crossover second toe deformities, using the anatomic grading system, progressive anatomic changes from lateral to medial were found, and the authors believed that this classification could assist pre-operative planning and performance of a surgical repair [21].

Multiple methods for correction of gross MTP joint instability have been described. The Weil osteotomy technique and the flexor-to-extensor tendon transfer are the most common [10, 22, 23]. Only recently, surgeons have advocated correcting the MTP joint instability by direct repair of the PP [2, 24‐26]. Few of these reports use some type of classification to stratify the grade of MTP instability. The Weil osteotomy technique, on its own, has been one of the mainstays of surgical treatment for lesser MTP instability. In a prospective study with 7 years of follow-up, Hofstaetter et al. found 88 % patient satisfaction rate [23]. However, this author demonstrated 12 % of re-dislocation and 68 % incidence of floating toe. In a recent literature review, Highlander et al. [27] indicated that the floating toe was the most common complication of the Weil procedure, with a reported incidence average of 36 %.

The other current option in the literature is the flexor-to-extensor transfer. Gazdag and Cracchiolo [28] reported 35 % of fair results in a series of 20 feet, which were submitted to a flexor-to-extensor transfer. The relative success was attributed to post-operative stiffness. Myerson and Jung [29] reported on their retrospective group of 64 feet that underwent the same procedure and demonstrated that 34 % of patients had either major reservations or were unhappy with the outcome. Although several studies have confirmed the effectiveness of a flexor-to-extensor transfer, these investigations report variable levels of patient satisfaction, with results ranging from 51 % to 89 %. Also, incomplete correction after tendon transfer in patients with subluxated MTP joints has also been reported in the literature [30].

Direct repair of the plantar plate has gained recent attention, and this tendency is driven by the relatively poor results obtained in the treatment of these deformities, most of the time followed by high rates of failure and recurrence. A prospective study showing the results of direct open PP repair (grades 2 and 3 of the anatomical classification) presented a post-operative AOFAS forefoot score of 92 points on average and more than 68 % of the stable joint [8]. There was no joint instability recurrence reported.

Until now, we have only found reports that address how to treat the extensive plantar plate and collateral ligament tears with gross instability and obvious clinical presentation. The early stages of the pathological process, involving less extensive lesions and a subtle instability, have no current treatment options suggested in the literature. A delayed evaluation and treatment of plantar plate tears is quite common due to the lack of clear diagnosis in the early phases. Conservative treatment is frequently instituted and is effective in reducing the inflammatory period, but is not able to prevent both the progressive insufficiency and the failure of the plantar plate as a joint stabilizer [6, 11].

To the best of our knowledge, this series is the first to present a treatment option for subtle MTP joint instability. In pre-operative analyses, none of our patients had a completely stable joint and more than 97 % had grade 1 instability. With the combination of radiofrequency and Weil osteotomy, 83 % of the MTP joints were totally stable (grade 0) with more than 97 % congruent joints. We observed that 80 % of patients had a positive toe purchase test post-operatively and 94 % of them presented with toe touching of the ground with no residual elevation during our post-operative observation. The results obtained in grades 0 and 1 of PP tears were superior to those reported in grades 2 and 3 previously. This may indicate that treating MTP joint instability in the early stages could produce a better prognosis.

Although radiofrequency has been used in a large number of patients and different joints, this treatment is still controversial. On the basis of short-term clinical follow-up, the results of thermal capsulorrhaphy have shown both supportive and non-supportive outcomes [16, 31]. Thermal capsular shrinkage has become a common procedure for a variety of joint conditions usually associated with instability [12]. Some histologic studies demonstrate evidence of tissue repair and remodeling, rather than degeneration and necrosis, during a period of 3.5–62 months after thermal capsulorrhaphy [16, 32]. Success rates of thermal capsulorrhaphy seem to vary according to patient populations, thermal techniques, adjuvant procedures, and rehabilitation protocols. Electrothermal collagen shrinkage (ECS) in larger joints such as the shoulder and knee has resulted in disappointment [31]. In contrast, ECS has been used successfully in hand surgery and ankle lateral ligament repair [16, 33]. Some authors have clarified that thermal contraction of the anterolateral capsular-ligamentous structures of the ankle is quite similar to an anatomic repair type procedure [12, 15]. The molecular effects of RF energy on soft tissue have been described in numerous reports [15, 17, 33, 34]. One of the most important effects of RF energy is its great ability to shorten collagenous structures; hence, thermal capsulorrhaphy has been shown to produce an effective reduction in capsular volume and joint translation. Due to the biomechanical weakness of the thermally treated capsule, some authors have proposed post-operative immobilization to avoid the thermally altered joint capsule stretching before the completion of the biological repair process [12, 15, 34, 35]. For this reason, we decided to maintain our patients with the affected toes in plantar flexion for 6 weeks.

The limitations of our study could be the small number of patients analyzed, the absence of a control group, and the minimum follow-up period of 12 months. In our study, we described a new treatment for mild plantar plate tears with subtle instability, and during our follow-up, there was no progression or recurrence of the instability. Based on these findings, one could infer that diagnosing and treating instability of the lesser MTP joints in the early stages could prevent progression of the disease.

The combination of radiofrequency shrinkage of the plantar plate and distal Weil metatarsal osteotomy is a viable option in the treatment of the early stages (grades 0 and 1) of lesser metatarsophalangeal joint instability.