Clinical and radiological midterm outcome after treatment of pilonoidal fracture dislocations of the proximal interphalangeal joint with a parabolic dynamic external fixator

Excessive axial load to the finger can cause a fracture dislocation of the proximal interaphalangeal (PIP) joint. The middle phalanx is impacted at the head of the proximal phalanx, fracturing the articular surface of the base of the middle phalanx. A palmar, a dorsal, and/or an impressed central fracture fragment can occur depending on the load transition. In cases of fracture dislocation or joint subluxation, surgical treatment seems mandatory for a satisfactory result.

Different surgical treatment options have been described including extension block pinning, open reduction and internal fixation (ORIF) with screws or plating, percutaneous Kirschner (K)-wire pinning after closed or mini-open reduction, and various different external traction fixation systems including K-wires, rubber bands, and springs [1‐3].

Because open reduction and fixation is difficult and may lead to fragment necrosis, closed reduction including traction systems is favored. These systems allow early mobilization, whereas the immobilization of the PIP joint results in stiffness with a reduced range of motion due to periarticular scarring [4]. The use of an external traction fixator is based on reduction through traction of the fracture components and ligamentotaxis within the PIP joint to correct any subluxation of the joint [5‐10]. Good clinical and radiological results can be expected if anatomical alignment and congruity of the joint can be restored together with sufficient stability for early joint mobilization. There are limited data in the literature regarding the outcome of an external traction fixation system which uses K-wires without rubber bands or springs.

The purpose of this retrospective study was to evaluate the clinical and radiological midterm outcome of the parabolic external dynamic fixation system described by Syed et al. [7] used for pilonoidal PIP joint fracture dislocation injuries.

All patients with a fracture dislocation of the PIP joint who were treated with a dynamic external fixator at our institution between 2005 and 2015 were enrolled in this study. Inclusion criteria include a multifragmented and displaced base fracture of the middle phalanx with an articular impression including more than 40% of the joint surface, and/or a dorsal subluxation of the middle phalanx and surgical treatment at our institution.

Twenty-five patients met the inclusion criteria; however, only 21 patients (6 male, 15 female, mean age 37.7 years; range 15–73 years) were available for the final follow-up. All patients were treated with the dynamic external fixator described by Syed et al. [7].

Mean follow-up time was 25.5 months (SD 20.4). The dominant hand was affected fourteen times (66.7%). The index and middle finger were affected once, the ring finger 11, and the small finger 8 times. The frequency of the injury mechanism is shown in Table 1.

The mean time until surgery was 2.8 days (SD 2.94) after the injury. Ten patients had a palmar displaced fragment which was reduced and fixed with one or two additional 0.8 mm K-wires.

Occupational therapy-guided mobilization of the joint was conducted for an average of 27.1 units (SD 9.8; range 8–42). The external fixator was removed in our outpatient center after a mean period of 35.2 days (SD 6.2 days; range 25–50 days).

These results demonstrate that a parabolic dynamic external fixator leads to good clinical and radiologic outcomes in the treatment of pilonoidal PIP joint fracture dislocations.

Promising results are reported using dynamic external fixators by various authors [6, 7, 11‐13]. These fixators are advantageous as they allow early motion after surgery avoiding immobilization of the PIP joint, which is the most significant reason for a diminished range of motion [14]. A dynamic external fixator shows beneficial effects on ligamentotaxis realigning the fracture fragments. The applied traction, helped to maintain the disimpacted joint fragment, and the concentric joint position and allowing early joint motion. Moreover, it allows reshaping of the articular surface without compromising the fragile blood supply of the fracture fragments [7]. In our study, twelve patients (57%) showed anatomic alignment, seven a minor step off, one with a deepend articular cavity, and one patient with a subluxed position due to a pin tract infection. All but the latter were stable and showed a concentric joint at the time of final follow-up.

There are several different fixator designs described in the literature [5‐8, 13, 15‐17]. No major difference in the outcome of the simpler designs compared with the more expensive and sophisticated devices has been described [18]. The present study used a simple and cheap system, only consisting of two K-wires (app. costs < 10 Euro). The main advantage of this design is its simplicity, the limited amount of required hardware, and the possibility for uncomplicated postsurgical readjustments if necessary. An imperfectly placed K-wire can be corrected through changes of the radius of the curvature. Furthermore, there is the possibility to modify the external fixator under image intensifier and without anesthesia if the joint alignment is unfavorable or there is a secondary displacement, which was necessary twice in our study cohort. Both patients healed satisfactorily with a good and pain-free range of motion. The authors faced additional difficulties attempting a secondary modification of the fixator using Suzuki’s technique [19] with K-wires and rubber bands. Fixator movement occurs at the point of contact of the two K-wires and not at the K-wire bone contact point during finger flexion, which is different to other fixator systems. This presumably accounts for a low infection and loosening rate. Numerous reports using external fixators showed a mean range of motion in the PIP joint between 64° and 91° similar to this report with app. 76° [14, 20‐22]. The patient cohort in this study showed a moderate acceptance of the external fixator, however, a high satisfaction at final follow-up with very mild discomfort (VAS 0.7). These findings were backed by good functional scores.

Postoperative osteoarthritic changes after treatment with external dynamic fixators develop in 12.5–61% of the cases ranging from mild to moderate changes [7, 8, 23]. In most of the studies, small residual articular step offs are described, which may cause osteoarthritic changes. However, there seems to be no clear association between residual articular step offs and the extent of osteoarthritic changes. Several authors described a short- or long-term remodeling capacity of the injured PIP joint [19, 24, 25]. The present study cohort showed 12 PIP joints anatomically remodeled without any residual intraarticular step off at the time of final follow-up. Seven of the patients still had an articular step off of less than 1 mm. In 14 cases, a residual step off at the time of fixator removal was seen, but was not found on the radiographs at final follow up (Fig. 9a, b). 85.7% of our patients had minimal to severe osteoarthritic changes. However, as the pain level was very low, these osteoarthritic changes did not appear to be symptomatic. This emphasizes the findings of the previous studies which describe an ongoing articular PIP joint remodeling after the removal of the external fixator and no clear correlation to subsequent osteoarthritic changes [19, 24, 25].

The limitations of this study are its retrospective design, the short follow-up period, and the relatively small number of patients, in accordance with other studies. In addition, as this was a cohort study, there was no control group using a different treatment method. As most patients displayed osteoarthritic changes to some extent, long-term follow-up investigations appear necessary to identify patients who show an ongoing increase in osteoarthritis of the PIP joint and possible ongoing reduction of the range of motion.

The primary results of this report show that the use of a parabolic dynamic external fixator constructed from two K-wires restores joint alignment and stability in unstable pilonoidal PIP joint dislocation fractures. It is a cost-effective alternative to other fixator designs and is associated with a good clinical outcome.