Percutaneous Fixation of Unstable Proximal Phalanx Fractures: A Biomechanical Study

Introduction

Proximal phalanx fractures are among the most common injuries to the hand. It is estimated that 23% of hand fractures occur in the phalanges. ¹ Various treatment methods exist for proximal phalangeal shaft fractures. Truly nondisplaced and stable fractures may be treated nonoperatively, while displaced and unstable fractures that cannot be successfully treated with a closed reduction will require operative intervention. ² While many methods of surgical treatment have been described in the literature, the ideal method of surgical fixation has not been determined. Closed reduction and intramedullary percutaneous pinning is an option in fractures that are amenable to pin fixation, such as transverse or short oblique fractures that are noncomminuted and are stable once the apex volar angulation has been corrected.^3,4 Comminuted fractures, long oblique, or spiral fractures are often treated by open reduction and screw and/or plate fixation to maintain length and alignment.^2,5 Both apex volar angulation and axial impaction at the fracture site will result in an extensor lag at the proximal interphalangeal (PIP) joint owing to relative lengthening of the unforgiving extensor mechanism over the proximal phalanx. Some authors have also used closed reduction and intramedullary percutaneous pin fixation to treat axially unstable proximal phalangeal shaft fractures that have some comminution with good results.^3,4

There are 2 common methods of closed reduction and intramedullary percutaneous fixation. The first is a transarticular pin technique, whereby the Kirschner wire (K-wire) is placed through the metacarpal head and metacarpophalangeal (MP) joint into the medullary canal of the proximal phalanx up to the subchondral bone of the proximal phalanx head, a technique popularized by Belsky et al. ⁶ The second is a periarticular technique where the K-wire is initially placed into the radial or ulnar base of the proximal phalanx, avoiding the MP joint, and inserted into the canal until fixation into the distal fragment is achieved.^7,8 This is then repeated on the other side of the MP joint so that 2 crossed pins transfix the fracture. Both techniques ideally engage the distal proximal phalanx subchondral bone. Axial shortening of the proximal phalanx can occur either if the K-wires protrude distally or proximally, usually proximally. It was our hypothesis that the trans-articular pinning technique could theoretically better maintain bony length in axially unstable fractures (spiral, long oblique, or comminuted fracture patterns) owing to the Kirschner wire’s passage through the metacarpal head in addition to the proximal phalanx base. Passing the K-wire through the metacarpal head, in addition to the base of the proximal phalanx could potentially create somewhat of a “locked” construct to better maintain proximal phalanx length, assuming frictional resistance to K-wire sliding is increased by passage through the metacarpal head. The peri-articular technique has only one point of proximal purchase, which is on the base of the proximal phalanx.

The biomechanical properties of these two techniques have not been studied to date. The goal of this cadaveric study is comparing the ability of these techniques to resist shortening in an axially unstable proximal phalanx shaft fracture model. Our hypothesis is that the trans-articular pinning technique will resist shortening better than the crossed pin technique and have more resistance than the periarticular technique.

Materials and Methods

Fresh frozen cadaveric hands (11 left, 6 right) were used for this study. After the hands were appropriately thawed, they were disarticulated at the level of the carpometacarpal joints of the second through fifth digits. The first rays were completely removed. The index, middle, and ring fingers were used for testing. The small fingers were excluded because of their small size. The second, third, and fourth digits are closer in size, therefore minimizing the factor of the size differences.

A mid-lateral incision was made on the radial border of each digit at the level of the proximal phalanx, leaving all of the ligaments and soft tissues intact. Once the bone was exposed, a 5 mm segment was measured and carefully resected using a sagittal saw from the level of the mid-shaft of the proximal phalanx; the kerf of the blade was taken into consideration during this resection so a total of 5 mm was resected in each finger. The osteotomies were transverse. Three percutaneous pin fixation techniques were employed and randomized for each finger. The first technique was the transarticular pin using a single 1.1 mm Kirschner wire placed antegrade through the metacarpal head and MP joint into the proximal phalanx up to the level of the subchondral surface of the PIP joint (Figure 1). The second technique used the same transarticular pinning method, except that a second 1.1 mm K-wire was added for additional fixation (Figure 2). The third technique was the crossed pinning technique where a 1.1 mm K-wire was placed at the base of the proximal phalanx, just lateral to the articular surface and inserted antegrade into the canal, across the fracture site until purchase was obtained in the distal fragment in the region of the subchondral bone at the head of the proximal phalanx. After passage of the first wire, a second 1.1 mm K wire was placed on the other side of the joint and passed the same way into the distal fragment (Figure 3). All 3 techniques were repeated in each hand, randomized to different fingers. A GE OEC 6800 Mini C-arm was used to ensure proper positioning of the K-wires. The skin was sutured together at the conclusion of the procedure.

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Figure 1.

(a) anteroposterior and (b) lateral x-rays of the single transarticular pin technique.

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Figure 2.

(a) anteroposterior and (b) lateral x-rays of the double transarticular pin technique.

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Figure 3.

(a) anteroposterior and (b) lateral x-rays of the periarticular pin technique.

The hand was securely clamped in a customized jig (Figure 4). Each digit was attached to the jig with a customized holder in a position of 90° of flexion at the PIP joint. Loads were then applied to the digit using an Instron 5848 MicroTester (Norwood, Massachusetts). The phalanx was first preconditioned with cyclic loading to best simulate real, postoperative clinical conditions. A 5 N tare load was applied to the proximal phalanx, and the digit underwent cyclic loading with a triangular waveform at a frequency of 0.05 Hz and amplitude of 1 mm of for 10 cycles. The 10 cycles served to precondition the finger after reinserting the crushed bone back inside the finger. ⁹ This resulted in cyclic loads with an amplitude of approximately 20 N. After cyclic loading, the digit was axially loaded at a constant displacement rate of 0.5 mm/s to determine construct subsidence as a function of axial load while in the pinned state. The axial load and energy applied (area under the force-displacement curve) at 1 mm, 2 mm, 3 mm, 4 mm, and 5 mm of axial subsidence were measured, representing increasing loads experienced during occupational therapy as a patient recovers.

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Figure 4.

Photographs.

To determine the effect of technique on fracture stability, one-way analysis of variance (ANOVA) (SAS, Cary, North Carolina) with technique as a repeated measure (each technique was performed on the same hand, randomized for different fingers) was performed for axial load and energy as a function of degree of subsidence. One-way multivariate analysis of variance (MANOVA) (SAS) with finger as a repeated measure was performed for axial load and energy as a function of amount of subsidence to determine if finger type had an effect. Tukey range tests were performed for posthoc analyses to discern statistical differences between techniques. Statistical significance was defined as P < .05. Data are presented as a mean ± SD. Posthoc power analyses were performed for technique and finger type using the PASS power analysis software (NCSS, Kaysville, Utah).

Results

Compressive forces versus degree of subsidence for each pinning technique are provided in Figure 5a. Energy required versus degree of subsidence for each pinning technique is provided in Figure 5b. There was no significant difference in force or energy by pinning technique at any level of subsidence (Table 1). As to be expected, greater amounts of shortening required larger forces. A posthoc power analysis for the subsidence force by technique found an average power of 83% for the 5 levels of subsidence for a 25% difference in the mean with P = .05. Similarly, an average power of 93% was found for the energy of subsidence.

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Figure 5.

(a) Compressive force versus subsidence by pinning technique. (b) Energy versus subsidence by pinning technique.

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Table 1.

P values When Comparing Pinning Techniques for Axial Force and Energy by Level of Subsidence.

Axial displacement	Axial force	Energy
1 mm	0.388	0.311
2 mm	0.701	0.621
3 mm	0.746	0.723
4 mm	0.586	0.774
5 mm	0.816	0.812

Compressive forces versus degree of subsidence for finger type are provided in Figure 6a. Energy required versus degree of subsidence for finger are provided in Figure 6b. No differences in force and energy required for subsidence were found for finger type (Wilk’s lambda, P = .741). A posthoc power analysis for the subsidence force by finger type found an average power of 85% for the 5 levels of subsidence for a 25% difference in the mean with P = .05. Similarly, an average power of 92% was found for the energy of subsidence.

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Figure 6.

(a) Compressive force versus subsidence by finger type. (b) Energy versus subsidence by finger type.

Discussion

Unstable proximal phalangeal shaft fractures are common injuries whose ideal treatment has not yet been definitively determined. Smooth pin fixation has been a common treatment method utilized by orthopedic surgeons for phalangeal fractures;^2,10 however, it can be associated with a high complication rate.

Sela et al performed a cadaveric study (n = 4) to quantify the effect of K-wire placement in the region of the MP joint on PIP joint motion. The authors report that insertion of the K-wire through the tendon resulted in 34° loss of flexion, compared to 17° loss of flexion with lateral insertion of the K-wire, and 12° loss of flexion with the K-wire inserted at the midaxial line. ¹¹

Botte et al reported on 137 patients treated with 422 pins over a 4-year period for hand and wrist fractures. There was an overall complication rate of 18%, with 69% of those attributed to pins placed for phalangeal fractures. ¹⁰ There are reports of high complication rates with both of the techniques described: transarticular and periarticular. Faruqui et al retrospectively reviewed 50 patients treated with either transarticular or periarticular pinning for phalangeal shaft fractures and found an overall complication rate of 56% and 48%, respectively. The most common complications were loss of motion and flexion contractures at the PIP joint. The transarticular group also required more secondary procedures; however, their overall complication rates were not statistically different. ¹²

Despite the complications, several studies have described good clinical outcomes with both pin fixation methods. Belsky et al ⁶ described 100 patients with phalangeal shaft fractures with 90% good to excellent results using the transarticular method. Furthermore, Hornbach and Cohen ⁴ had excellent results in 10 of 12 patients treated using this same method. Eberlin et al ³ reported on a series of 41 patients with proximal phalanx fractures treated using solely the periarticular pin fixation method, with 80% achieving a good to excellent result. Additionally, Saied and Sabet Jahromi conducted a prospective study on 61 patients with proximal phalanx transverse or short oblique fractures. Ultimately, when comparing those with cross pinning (n = 31) to those with parallel pins (n = 21), there were no significant differences between the groups. Furthermore, both groups demonstrated significant improvement in range of motion at 3- to 6-months of follow-up. ¹³

We compared the biomechanical strength of pin fixation methods with the hypothesis that the transarticular method would be better able to resist shortening given that the pin or pins are “friction-anchored” into the fixed and uninjured metacarpal head. However, our results showed that when comparing techniques, there was no significant difference between pinning techniques. The same methodology was used on 3 different fingers, but when comparing between technique, the results remained similar. Furthermore, this is relevant clinically as it demonstrates that the less technically challenging method utilizing a single pin, the transarticular method, may be just as effective as using an additional pin or when using the periarticular method. This can aid surgeon decision making when approaching a proximal phalanx fracture that is indicated for closed reduction and percutaneous pinning.

Conclusion

Proximal phalanx fractures can be treated using closed reduction and percutaneous pin fixation with any of the techniques described. While we do not recommend any one technique over the others based on the current biomechanical data, an important finding is that the single pin method is as effective as using additional pins for fixation with respect to resistance to axial shortening. Future investigations should include a prospective, randomized clinical trial to validate these results in a clinical setting. Subsequent randomized controlled trial clinical studies on these three techniques should evaluate not only construct stability, but also PIP joint contracture and tendon adhesion rates, total active motion, and secondary re-operation rates (joint release/tenolysis).