Calcaneal fractures, common foot injuries often resulting from high-energy trauma, presents great clinical challenges due to their complex anatomical structure and post-traumatic sequelae (1). Sanders (2) developed a computed tomography–based classification to assist decision-makings and preoperative planning. Conservative treatment, such as using Plaster-of Paris, might be considered in fractures with little displacement (Sanders type I) or compromised soft-tissues. Surgical intervention is typically preferred for displaced intra-articular calcaneus fractures (DIACFs), which accounts for approximate 75% of calcaneal fractures (3, 4). In recent years, various minimally invasive techniques were developed and applied to improve DIACFs treatment. In comparison with traditional open surgery, minimally invasive surgery (MIS) showed advantages in minimizing iatrogenic tissue disturbance and incision-related complications while pursuing fracture reduction and fixation (5). However, the MIS approach is difficult to realize adequate fracture reduction and posterior facet realignment because of a limited visualization and percutaneous performance, leading to ongoing debate in this field (6, 7).

Calcaneal distractor as the imperative assistive instruments plays an key role in MIS for DIACFs and, to a certain extent, closely determines the surgical outcomes (8). To facilitate fracture distraction and improve surgical outcomes, we designed a novel calcaneal distractor (National Invention Patent) based on the principle of ligamentotaxis (9). The tailored new calcaneal distractor (Figure 1) basically consists of two traction pins, two distraction assemblies, and a “T”-shaped handle. Each distraction assembly includes a fixed support rod, a connecting rod, a sliding support rod, and a threaded support rod, with a threaded sleeve in the sliding support rod. By rotating the “T” handle, the threaded support rod is mechanically driven to move forward in the threaded sleeve. When the front end of the threaded support rod contacts the fixed support rod, based on the principle of action and reaction, the sliding support rod is pulled away from the fixed support rod, bilaterally achieving a multi-dimensional distraction.

At our institution, this tailored distractor was frequently applied to assist MIS for DIACFs. This paper aimed to assess its efficiency of the tailored calcaneal distractor in percutaneous minimally invasive treatment for Sanders II and III type calcaneus fractures and report the surgical outcomes during a 2-year follow-up.

Perioperatively, all feet (39 Sanders type II and 24 Sanders type III fractures) successfully achieved fracture reduction with the interval between injury to operation average 1.3 days, the duration of operation average 40.1 min, and the hospital stay average 4.9 days (Table 1).

Radiographic measurements revealed significant differences between pre-operation and post-operation in calcaneus width (43.7 ± 4.7 vs. 33.2 ± 1.9, p < 0.05) and height (37.0 ± 1.9 vs. 43.2 ± 2.0, p < 0.05), while no differences between post-operation and the normal side (p > 0.05). The length was comparable between pre-operation, post-operation, and the normal side (p > 0.05) (Table 2). Böhler's angle at the final follow-up was significantly improved from pre-operation measurements (34.0 ± 2.6 vs. 11.1 ± 2.1, p < 0.05), so as to Gissane's angle (122.7 ± 3.8 vs. 99.8 ± 3.9, p < 0.05), while no significant differences were detected between the post-operative and the contralateral side Bohler's angle and Gissane's angle (p > 0.05, respectively) (Table 2).

At the last follow-up, the AOFAS score was significantly improved from preoperation (81.4 ± 7.6 vs. 51.2 ± 3.1, p < 0.05), with classification distributed as 39 excellent, 21 good, and 3 fair classification, resulting in an excellent and good rate of 95.2%. The VAS score was significantly decreased from preoperation (1.3 ± 1.0 vs. 7.3 ± 1.4, p < 0.05) at the last follow-up (Table 3).

Additionally, the reduction quality of the posterior subtalar joint surface, as evidenced on CT images, were confirmed as Anatomical or near-anatomical realignment. Four feet (6.34%) encountered postoperative complications: one case got caught in transient symptoms of sural nerve injury, one case encountered a screw rupture 2 months after surgery without further detrimental effects, and two cases developed degenerative changes of the subtalar joint.

Illustration case Please see Figure 4.

The treatment of displaced intra-articular calcaneal fractures (DIACFs) presents a clinical dilemma where the optimal techniques remain debating (11, 12). Recently, minimally invasive surgery (MIS) reportedly had advantages in minimal invasion and lower risk of would-related complications over conventional open surgery or semi-closed reduction, such as sinus tarsi approach (STA) (13–15). However, less precise reduction of calcaneal fractures limited the application of MIS for DIACFs (3). Notably, the tailored distractor-assisted MIS described in this study demonstrated a balance between minimal invasion and adequate reduction and reliable fixation of calcaneal fractures via percutaneous manner. With all surgical steps handily reproducible and performed without exposing the surgeon to x-rays, our interpretation of this technique would greatly contribute to its widespread adoption in hospitals.

The primary goal of calcaneal fracture treatment is to achieve anatomy reduction and reliable fixation (16). Technically, percutaneous minimally invasive techniques for DIACFs imperatively require adjuvant tools to assist fracture distraction and fixation via percutaneous maneuver. In addition, the irregular shape of the calcaneus and the varied displacement patterns of the fractures render MIS more challenging (9). In such settings, many auxiliary devices have been successively innovated and applied in MIS for calcaneal fractures. Traditionally, Steinmann pins or Schanz screws were used to traverse the posterior calcaneal tuberosity, restoring the length of the calcaneus and correcting varus and valgus deformities through manual traction (17). The traction force is limited and cannot sustain the reduction, and surgeons often have to work directly under x-ray exposure. Driessen et al. (11) was among the first to use a three-point distractor to assist minimally invasive treatment of calcaneal fractures, a technique later adopted by other researchers. Despite some improvements, their distractor had a complex structure with inconvenient operablity. Zhao et al. (18) used a single Steinmann pin distractor placed on the lateral side of the affected foot, combined with a sinus tarsal incision, to treat calcaneal fractures. Such a distractor, which operates in an arc, is not fully effective in its distracting role, and a unilateral distractor might cause calcaneal varus or valgus deformities due to its eccentric traction force. Recognizing bilateral distractors superior to unilateral ones in correcting varus and valgus deformities, Dayton et al. (19) used an Ilizarov external fixator to assist in reduction, combined with bilateral small external fixators for percutaneous fixation of calcaneal fractures. This distractor is more complex and obstructs intraoperative fluoroscopy. Two-point distractor are generally adopted to bilaterally reduce calcaneus fracture ever after (20, 21). Although those MIS techniques vary widely, mal-reduction, no hand-free distraction, reduction loss, and occupation of operation space were the major drawbacks emerging in the former clinical practices.

Developed but different from the principle of ligamentotaxis, we designed a self-constructed calcaneal distractor with integrated structures to makes up for the shortcomings of former distractors. The tailored distractor we constructed harbors the following advancements and innovations (Please refer to Figures 1, 2): First, it has a simple structure, including two traction pins, two sets of retraction components, and a “T”-sharped handle. The traction pins are 3.0 mm diameter ordinary Kirschner wires, which are resistant to deformation ensuring effective retraction. The “T” handle is detachable, leaving more operating space. Second, it is easy to operate. The insertion points of the Kirschner wires are located at the center of the talar neck and the center of the calcaneal tuberosity, avoiding important blood vessels, nerves, and tendons. The two insertion points are on the long axis of the calcaneus, maximizing the effect of ligamentotaxis; by simply rotating the “T” handle, the fracture ends of the calcaneus can be effectively retracted mechanically. Third, it provides strong retraction force bilaterally and aids significantly in reduction. Once the retractor is installed, the medial and lateral retraction components can be adjusted to varying degrees per characteristic displacement patterns. The length and height of the calcaneus can be quickly restored, synergistically with the inversion and/or eversion deformities correction. Fourth, it can stably maintain the retracted state without obstructing fluoroscopy. Once the calcaneal fracture ends are retracted, enough sub-talar space is provided, facilitating the realignment of subtalar joint surface. Fifth, all operations can be performed without exposure to x-rays for operators. Given those characteristics, we hypothesized that our distractor is ideally modified to facilitate the percutaneous maneuver and improves surgical outcomes in DIACFs treatment.

As a result, all cases in the present study were successfully managed by our distractor-assisted reduction and percutaneous cannulated screw fixation. The tailored-assisted MIS showed advantages in the interval from injury to surgery, operation time, and the hospital stay when comparing with other reports regarding conventional STA or open approach reduction (22–24). Notably in our practice, the tailored distractor-assisted MIS are particularly appropriate for Sanders II and III calcaneus fractures earlier in the post injury period irrespective of the skin blister. As comparable with other minimally invasive techniques noted rare wound complications (6, 15, 17), our cases had not encountered any wound-related complications. Schepers (25) published a systemic review regarding sinus tarsi approach (STA) in DIACFs and found that wound complications were reported in all studies with a rate average 4.8%. A conspicuous advantage of MIS in comparison with conventional STA approach for DIACFs is the earlier surgical intervention and minimal invasion. The earlier intervention enables timely and effective fracture reduction, benefiting the subsequent rehabilitation progress (26–28). Additionally, the percutaneous approach results in less scar tissue formation around the ankle and subtalar joints, both contributing to the lower risk of developing wound-related complications and other degenerative changes of subtalar joint, which were common complications reported in other studies (29, 30). Judging from the surgical outcomes, our MIS strategy could effectively minimize iatrogenic tissue disturbance and incision-related complications while pursuing fracture reduction and fixation in comparison with traditional open or STA methods.

As discussed above, the current existing MIS techniques reflect a noteworthy drawback of inadequate reduction because of the limited visualization and indirect maneuver (31–33). Various imaging parameters of the calcaneus are available to evaluate the quality of fracture reduction, especially Gissane's angle and Böhler's angle, which are closely related to postoperative functional outcomes (34). Gavlik et al. reported reduction collapse or loss when using screws alone to fix calcaneal fractures, while this issue did not occur in our study (30). Recently, Zhang presented a T-handles rod distractor, screwed together with a cannulated screw, to assist reduction for the joint depression-type of calcaneal fractures via STA (35). They reported reduction failure because the distractor cannot hold the calcaneal tuberosity tightly or the inner rod could puncture the subtalar articular surface. In the present study, postoperative x-rays and CT scans showed complete restoration of the calcaneal length, width, and height, realignment of the collapse and displacement of the posterior subtalar joint surface, as well as complete correction of the varus or valgus deformity, both comparable with normal side indices. Adequate and precise fracture reduction achieved in this study could be partly explained by the tailored distractor providing powerful and multi-dimensional distraction force, which is outperform the AO two-point distractor offering retraction bilaterally (21). Furthermore, the technique underscored percutaneous distribution of cannulated screws. The screw placement configuration ensures a frame structure around the calcaneal “neutral triangle” to provide good initial stability conducive to fracture healing. Even in osteoporotic cases, our distractor seemed to be osteoporosis-friendly considering its structural features by distributing the force of distraction evenly via two 3.0 mm Kirschner wires and gently through bilateral threaded-rod adjustment, which definitely deserves future investigation to clarify this advantage in osteoporotic setting. Therefore, despite via percutaneous minimally invasive approach, our MIS strategy yielded comparable radiological outcomes and functional scores with conventional open or STA surgery (26, 36, 37) while outperforming other MIS techniques about this matter (4, 6, 20, 21). However, it should be cautious for utilizing this minimally invasive technique to treat Sander type IV fractures characterized by severe comminuted subtalar fragments. We have zero MIS experience dealing with Sanders type IV calcaneal fracture.

In conclusion, the tailored distractor demonstrated strong operability and effectiveness in fracture reduction. Subsequently, the distractor-assisted MIS for Sanders II and III calcaneus fractures realized adequate fracture reduction and reliable internal fixation, equivalent to conventional STA methods but a major previous limitations in other MIS techniques. As the implementation of ERAS (enhanced recovery after surgery) pathways developing (38), this study provides a promising therapeutic option for better DIACFs management. However, our study also has inherent limitations. As a retrospective study, it failed to set a control group, which compromised the interpretation of its clinical significance; Second, the follow-up period was short, making it difficult to evaluate long-term complications such as subtalar arthritis. Third, his study failed to interpret difference between Sanders II and III types because there were no enough cases to carry out subgroup analysis. Further randomized controlled studies with larger sample sizes and longer follow-up periods are needed.

Application of the tailored calcaneal distractor in MIS for Sanders type II and III calcaneal fractures has demonstrated advantages in effectively manipulating fracture reduction and yielding favorable clinical outcomes. Further cohort study is required to clarify its clinical significance vs. other techniques.